Amended add_reaction documentation to messages.py
@@ -546,7 +546,12 @@ class Message(snowflake.Unique):
Parameters
----------
emoji : builtins.str or hikari.models.emojis.Emoji
- The emoji to add.
+ The emoji to add. This may be a unicode emoji string, the
+ `name:id` of a custom emoji, or a subclass of
+ `hikari.models.emojis.Emoji`.
+
+ Note that if the emoji is an `hikari.models.emojis.CustomEmoji`
+ and is not from a guild the bot user is in, then this will fail.
Examples
--------
