Clarify documentation for user_id parameter in Courses#users
Clarify documentation for user_id parameter in Courses#users

test plan:
 - check API documentation for the user_id parameter
   in the "List users in course" endpoint

fixes CNVS-30410

Change-Id: I65e93c152399d78741c508aaeec248e69a281a3a
Reviewed-on: https://gerrit.instructure.com/93004
Tested-by: Jenkins
Reviewed-by: James Williams  <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>
QA-Review: Deepeeca Soundarrajan <5bcd4b623f00b7fc2942cd1c65c245b30a48a61f@instructure.com>
Product-Review: Chris Ward <341ae4b10181e9ae5056162440771572020800f2@instructure.com>

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