Refactor Gas/Fee Model (#3258)

docs/gaia/gaiacli.md

@@ -128,6 +128,33 @@ gaiacli keys show --multisig-threshold K name1 name2 name3 [...]
 For more information regarding how to generate, sign and broadcast transactions with a
 multi signature account see [Multisig Transactions](#multisig-transactions).
 
+### Fees & Gas
+
+Each transaction may either supply fees or gas prices, but not both. Most users
+will typically provide fees as this is the cost you will end up incurring for
+the transaction being included in the ledger.
+
+Validator's have a minimum gas price (multi-denom) configuration and they use
+this value when when determining if they should include the transaction in a block
+during `CheckTx`, where `gasPrices >= minGasPrices`. Note, your transaction must
+supply fees that match all the denominations the validator requires.
+
+__Note__: With such a mechanism in place, validators may start to prioritize
+txs by `gasPrice` in the mempool, so providing higher fees or gas prices may yield
+higher tx priority.
+
+e.g.
+
+```bash
+gaiacli tx send ... --fees=100photino
+```
+
+or
+
+```bash
+gaiacli tx send ... --gas-prices=0.000001stake
+```
+
 ### Account
 
 #### Get Tokens