Update memo usage docs

docs/core/proto-docs.md

@@ -7625,7 +7625,7 @@ TxBody is the body of a transaction that all signers sign over.
 | Field | Type | Label | Description |
 | ----- | ---- | ----- | ----------- |
 | `messages` | [google.protobuf.Any](#google.protobuf.Any) | repeated | messages is a list of messages to be executed. The required signers of those messages define the number and order of elements in AuthInfo's signer_infos and Tx's signatures. Each required signer address is added to the list only the first time it occurs. By convention, the first required signer (usually from the first message) is referred to as the primary signer and pays the fee for the whole transaction. |
-| `memo` | [string](#string) |  | memo is any arbitrary memo to be added to the transaction |
+| `memo` | [string](#string) |  | memo is any arbitrary note/comment to be added to the transaction. In clients, any public exposing text should not be called as memo, should use `note` instead (see https://github.com/cosmos/cosmos-sdk/issues/9122). |
 | `timeout_height` | [uint64](#uint64) |  | timeout is the block height after which this transaction will not be processed by the chain |
 | `extension_options` | [google.protobuf.Any](#google.protobuf.Any) | repeated | extension_options are arbitrary options that can be added by chains when the default options are not sufficient. If any of these are present and can't be handled, the transaction will be rejected |
 | `non_critical_extension_options` | [google.protobuf.Any](#google.protobuf.Any) | repeated | extension_options are arbitrary options that can be added by chains when the default options are not sufficient. If any of these are present and can't be handled, they will be ignored |

docs/core/transactions.md

@@ -93,7 +93,7 @@ The `TxBuilder` interface contains data closely related with the generation of t
 
 - `Msg`s, the array of [messages](#messages) included in the transaction.
 - `GasLimit`, option chosen by the users for how to calculate how much gas they will need to pay.
-- `Memo`, to send with the transaction.
+- `Memo`, a note or comment to send with the transaction.
 - `FeeAmount`, the maximum amount the user is willing to pay in fees.
 - `TimeoutHeight`, block height until which the transaction is valid.
 - `Signatures`, the array of signatures from all signers of the transaction.

proto/cosmos/tx/v1beta1/tx.proto

@@ -74,7 +74,9 @@ message TxBody {
   // transaction.
   repeated google.protobuf.Any messages = 1;
 
-  // memo is any arbitrary memo to be added to the transaction
+  // memo is any arbitrary note/comment to be added to the transaction.
+  // In clients, any public exposing text should not be called as memo,
+  // should use `note` instead (see https://github.com/cosmos/cosmos-sdk/issues/9122).
   string memo = 2;
 
   // timeout is the block height after which this transaction will not