docs: Update models/_docs/docs.md

Co-authored-by: Ty Hob / Brian Mesick <112640379+bmtcril@users.noreply.github.com>

models/_docs/docs.md

@@ -1,6 +1,9 @@
 
 {% docs actor_id %}
-The xAPI actor identifier
+The "id" portion of the xAPI Actor for this event. See: https://xapi.com/statements-101/#actor
+
+The LMS can be configured to send different identifiers for an actor, but they are all stored as Strings in ClickHouse: https://docs.openedx.org/projects/openedx-aspects/en/latest/technical_documentation/how-tos/changing_actor_identifier.html
+
 {% enddocs %}
 
 {% docs block_id %}