Clarify Governor Bravo compatibility scope (#4090)

Co-authored-by: Francisco <fg@frang.io>

docs/modules/ROOT/pages/governance.adoc

@@ -20,7 +20,9 @@ The ERC20 extension to keep track of votes and vote delegation is one such case.
 
 === Governor & GovernorCompatibilityBravo
 
-An OpenZeppelin Governor contract is by default not interface-compatible with GovernorAlpha or Bravo, since some of the functions are different or missing, although it shares all of the same events. However, it’s possible to opt in to full compatibility by inheriting from the GovernorCompatibilityBravo module. The contract will be cheaper to deploy and use without this module.
+An OpenZeppelin Governor contract is by default not interface-compatible with Compound's GovernorAlpha or Bravo. Even though events are fully compatible, proposal lifecycle functions (creation, execution, etc.) have different signatures that are meant to optimize storage use. Other functions from GovernorAlpha are Bravo are likewise not available. It’s possible to opt in to a higher level of compatibility by inheriting from the GovernorCompatibilityBravo module, which covers the proposal lifecycle functions such as `propose` and `execute`.
+
+Note that even with the use of this module, there will still be differences in the way that `proposalId`s are calculated. Governor uses the hash of the proposal parameters with the purpose of keeping its data off-chain by event indexing, while the original Bravo implementation uses sequential `proposalId`s. Due to this and other differences, several of the functions from GovernorBravo are not included in the compatibility module.
 
 === GovernorTimelockControl & GovernorTimelockCompound