Update ADR + changelog

CHANGELOG.md

@@ -54,6 +54,7 @@ older clients.
 
 ### API Breaking Changes
 
+* (baseapp) [\#5865](https://github.com/cosmos/cosmos-sdk/pull/5865) The `SimulationResponse` returned from tx simulation is now JSON encoded instead of Amino binary.
 * [\#5719](https://github.com/cosmos/cosmos-sdk/pull/5719) Bump Go requirement to 1.14+
 * (x/params) [\#5619](https://github.com/cosmos/cosmos-sdk/pull/5619) The `x/params` keeper now accepts a `codec.Marshaller` instead of
 a reference to an amino codec. Amino is still used for JSON serialization.

docs/architecture/adr-020-protobuf-transaction-encoding.md

@@ -103,6 +103,11 @@ to handle all the types, but also knows how to generate transactions, signatures
 and messages.
 
 ```go
+type AccountRetriever interface {
+  EnsureExists(addr sdk.AccAddress) error
+  GetAccountNumberSequence(addr sdk.AccAddress) (uint64, uint64, error)
+}
+
 type Generator interface {
   NewTx() ClientTx
 }