refactor: Small clarifications to authz docs and one error description (#11506)

## Description

This small PR is trying to clarify the documentation that I found ambiguous when reading it.
Furthermore, it makes one error message more precise ("non-negative" --> "positive").

In particular:
 - I clarified that the field `AcceptResponse.Accept` will be set to `true` when an authorization is accepted, but **will not** be set to `false` otherwise (instead, the function `Accept` will return an error).
 - I clarified that the field `AcceptResponse.Updated` will not always be populated: it will be `nil` unless there are real changes to the authorization
 - I changed the error message in the `send_authorization.go` function, when `IsAllPositive()` returns `false` from _spend limit cannot be negitive_ to _spend limit must be positive_. I emphasized the fact that spend limit must be positive in the documentation.

This is my first contribution to the Cosmos-SDK codebase so if I made some mistake the process (wrt the checklist), guide me patiently, pls.



---

### 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...

- [x] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [x] added `!` to the type prefix if API or client breaking change
- [x] 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: NOTE: does not apply, these are clarification changes
- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules): NOTE: does not apply, these are clarification changes
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing): NOTE: does not apply, these are clarification changes
- [ ] added a changelog entry to `CHANGELOG.md`: NOTE: does not apply, these are clarification changes
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc) NOTE: does not apply, these are clarification changes
- [x] updated the relevant documentation or specification
- [x] 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/architecture/adr-030-authz-module.md

@@ -117,6 +117,15 @@ A different type of capability for `MsgSend` could be implemented
 using the `Authorization` interface with no need to change the underlying
 `bank` module.
 
+##### Small notes on `AcceptResponse`
+
+- The `AcceptResponse.Accept` field will be set to `true` if the authorization is accepted.
+However, if it is rejected, the function `Accept` will raise an error (without setting `AcceptResponse.Accept` to `false`).
+
+- The `AcceptResponse.Updated` field will be set to a non-nil value only if there is a real change to the authorization.
+If authorization remains the same (as is, for instance, always the case for a [`GenericAuthorization`](#genericauthorization)),
+the field will be `nil`.
+
 ### `Msg` Service
 
 ```proto

x/authz/spec/01_concepts.md

@@ -32,7 +32,7 @@ The Cosmos SDK `x/authz` module comes with following authorization types:
 
 ### SendAuthorization
 
-`SendAuthorization` implements the `Authorization` interface for the `cosmos.bank.v1beta1.MsgSend` Msg. It takes a `SpendLimit` that specifies the maximum amount of tokens the grantee can spend. The `SpendLimit` is updated as the tokens are spent.
+`SendAuthorization` implements the `Authorization` interface for the `cosmos.bank.v1beta1.MsgSend` Msg. It takes a (positive) `SpendLimit` that specifies the maximum amount of tokens the grantee can spend. The `SpendLimit` is updated as the tokens are spent.
 
 +++ https://github.com/cosmos/cosmos-sdk/blob/v0.43.0-beta1/proto/cosmos/bank/v1beta1/authz.proto#L10-L19
 

x/bank/types/send_authorization.go

@@ -45,7 +45,7 @@ func (a SendAuthorization) ValidateBasic() error {
 		return sdkerrors.ErrInvalidCoins.Wrap("spend limit cannot be nil")
 	}
 	if !a.SpendLimit.IsAllPositive() {
-		return sdkerrors.ErrInvalidCoins.Wrapf("spend limit cannot be negitive")
+		return sdkerrors.ErrInvalidCoins.Wrapf("spend limit must be positive")
 	}
 	return nil
 }