doc: clarify between owner/username in python lib

* provide clarification between username in python client lib which is
  the full username@example.com and owner which is username

Change-Id: I6b4c708307d2fe7d3f68a245e48edbbeda69bd18

Author: sadsfae

docs/quads-self-schedule.md

@@ -164,6 +164,9 @@ with QuadsApi(username, password, base_url) as quads:
 ```
 
 ### Create an assignment via Python
+> [!NOTE]
+> The `owner` field is the username minus the `@example.com` part of the email string, e.g. `joe`
+>
 ```python
 from quads_lib import QuadsApi