docs: make username propriety more findable (#493)

For regular twitch users, this propriety is known as `username`, but
the helix api definitions refer to as `login name`.

This makes it easier to find the relevant twitch api section from
reading the twitchio docs, and vice versa.

Co-authored-by: Danilo Rezende <[email protected]>

Author: returnDanilo

twitchio/user.py

@@ -88,7 +88,7 @@ class PartialUser:
     id: str | int
         The user's ID.
     name: str | None
-        The user's name. In most cases, this is provided. There are however, rare cases where it is not.
+        The user's name. Also known as *username* or *login name*. In most cases, this is provided. There are however, rare cases where it is not.
     display_name: str | None
         The user's display name in chat. In most cases, this is provided otherwise fallsback to `name`. There are however, rare cases where it is not.
     """
@@ -3459,7 +3459,7 @@ class User(PartialUser):
     id: str
         The user's ID.
     name: str | None
-        The user's name. In most cases, this is provided. There are however, rare cases where it is not.
+        The user's name. Also known as *username* or *login name*. In most cases, this is provided. There are however, rare cases where it is not.
     display_name: str
         The display name of the user.
     type: Literal["admin", "global_mod", "staff", ""]