docs: guidelines for ValidateBasic (#10983)

## Description

Closes: #10680

---

### Author Checklist

*All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.*

I have...

- [ ] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] added `!` to the type prefix if API or client breaking change
- [ ] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#pr-targeting))
- [ ] provided a link to the relevant issue or specification
- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing)
- [ ] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] updated the relevant documentation or specification
- [ ] reviewed "Files changed" and left comments if necessary
- [ ] confirmed all CI checks have passed

### Reviewers Checklist

*All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.*

I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed 
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)

docs/core/baseapp.md

@@ -224,7 +224,9 @@ transaction is received by a full-node. The role of `CheckTx` is to guard the fu
 Unconfirmed transactions are relayed to peers only if they pass `CheckTx`.
 
 `CheckTx()` can perform both _stateful_ and _stateless_ checks, but developers should strive to
-make them lightweight. In the Cosmos SDK, after [decoding transactions](./encoding.md), `CheckTx()` is implemented
+make the checks **lightweight** because gas fees are not charged for the resources (CPU, data load...) used during the `CheckTx`. 
+
+In the Cosmos SDK, after [decoding transactions](./encoding.md), `CheckTx()` is implemented
 to do the following checks:
 
 1. Extract the `sdk.Msg`s from the transaction.
@@ -237,9 +239,8 @@ to do the following checks:
    as `sdk.Msg`s are not processed. Usually, the [`AnteHandler`](../basics/gas-fees.md#antehandler) will check that the `gas` provided
    with the transaction is superior to a minimum reference gas amount based on the raw transaction size,
    in order to avoid spam with transactions that provide 0 gas.
-4. Ensure that each `sdk.Msg`'s fully-qualified service method matches on of the routes inside the `msgServiceRouter`, but do **not** actually
-   process `sdk.Msg`s. `sdk.Msg`s only need to be processed when the canonical state need to be updated,
-   which happens during `DeliverTx`.
+
+`CheckTx` does **not** process `sdk.Msg`s -  they only need to be processed when the canonical state need to be updated, which happens during `DeliverTx`.
 
 Steps 2. and 3. are performed by the [`AnteHandler`](../basics/gas-fees.md#antehandler) in the [`RunTx()`](#runtx-antehandler-and-runmsgs)
 function, which `CheckTx()` calls with the `runTxModeCheck` mode. During each step of `CheckTx()`, a
@@ -269,7 +270,7 @@ The response contains:
 #### RecheckTx
 
 After `Commit`, `CheckTx` is run again on all transactions that remain in the node's local mempool
-after filtering those included in the block. To prevent the mempool from rechecking all transactions
+excluding the transactions that are included in the block. To prevent the mempool from rechecking all transactions
 every time a block is committed, the configuration option `mempool.recheck=false` can be set. As of
 Tendermint v0.32.1, an additional `Type` parameter is made available to the `CheckTx` function that
 indicates whether an incoming transaction is new (`CheckTxType_New`), or a recheck (`CheckTxType_Recheck`).

docs/core/transactions.md

@@ -25,7 +25,7 @@ Transaction objects are Cosmos SDK types that implement the `Tx` interface
 It contains the following methods:
 
 - **GetMsgs:** unwraps the transaction and returns a list of contained `sdk.Msg`s - one transaction may have one or multiple messages, which are defined by module developers.
-- **ValidateBasic:** includes lightweight, [_stateless_](../basics/tx-lifecycle.md#types-of-checks) checks used by ABCI messages [`CheckTx`](./baseapp.md#checktx) and [`DeliverTx`](./baseapp.md#delivertx) to make sure transactions are not invalid. For example, the [`auth`](https://github.com/cosmos/cosmos-sdk/tree/master/x/auth) module's `StdTx` `ValidateBasic` function checks that its transactions are signed by the correct number of signers and that the fees do not exceed what the user's maximum. Note that this function is to be distinct from the `ValidateBasic` functions for `sdk.Msg`s, which perform basic validity checks on messages only. For example, when [`runTx`](./baseapp.md#runtx) is checking a transaction created from the [`auth`](https://github.com/cosmos/cosmos-sdk/tree/master/x/auth/spec) module, it first runs `ValidateBasic` on each message, then runs the `auth` module AnteHandler which calls `ValidateBasic` for the transaction itself.
+- **ValidateBasic:** lightweight, [_stateless_](../basics/tx-lifecycle.md#types-of-checks) checks used by ABCI messages [`CheckTx`](./baseapp.md#checktx) and [`DeliverTx`](./baseapp.md#delivertx) to make sure transactions are not invalid. For example, the [`auth`](https://github.com/cosmos/cosmos-sdk/tree/master/x/auth) module's `StdTx` `ValidateBasic` function checks that its transactions are signed by the correct number of signers and that the fees do not exceed what the user's maximum. Note that this function is to be distinct from `sdk.Msg` [`ValidateBasic`](../basics/tx-lifecycle.md#ValidateBasic) methods, which perform basic validity checks on messages only. When [`runTx`](./baseapp.md#runtx) is checking a transaction created from the [`auth`](https://github.com/cosmos/cosmos-sdk/tree/master/x/auth/spec) module, it first runs `ValidateBasic` on each message, then runs the `auth` module AnteHandler which calls `ValidateBasic` for the transaction itself.
 
 As a developer, you should rarely manipulate `Tx` directly, as `Tx` is really an intermediate type used for transaction generation. Instead, developers should prefer the `TxBuilder` interface, which you can learn more about [below](#transaction-generation).