added canvas to filter mentors (#409)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Documentation**
* Clarified “Filter Learners for Mentors” behavior and improved
wording/grammar.
* Added example usage for codio_custom_mentor_for and highlighted setup
with a prominent note.
* Introduced Canvas-specific setup steps (Observer linking workflow) and
cross-platform app configuration guidance with visuals.
* Added a “Custom parameters” reference for opening student assignments
directly from the LMS, covering user ID, email, role, and name fields,
with examples and platform support notes.
  * Minor formatting and punctuation improvements.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Co-authored-by: Lola Valente <lvalente@codio.com>

Author: LolaValente

source/instructors/admin/integration/lti-app.rst

@@ -121,12 +121,13 @@ Toggling **Hide Not Started Assignments** to "on" will suppress the display of a
 Filter Learners for Mentors
 ****************************
 
-Enabling **Filter Learners for Mentors** to "on" will allow you to only show Mentor/Observers specific students that you wish them to see/manage in the Codio course.
+Enabling **Filter Learners for Mentors** to "on" will allow you to show Mentor/Observers only specific students that you wish them to see/manage in the Codio course.
 
-To set this up, edit your LTI app as set up above or send as a custom parameter adding `codio_custom_mentor_for` as a custom field entering as the parameter either the students email addresses or their LMS user IDs.   To enter multiple students separate with comma (',')
+To set this up, edit your LTI app as set up above or send as a custom parameter by adding codio_custom_mentor_for as a custom field, entering as the parameter either the students' email addresses or their LMS user IDs. To enter multiple students, separate with commas (',').
 
 Example:
 
+
 .. code:: ini
 
    codio_custom_mentor_for="student1@email.com,student2@email.com"
@@ -136,8 +137,19 @@ Example:
 .. figure:: /img/lti/filter_learners.png
    :alt: Filter learners for mentors
 
-If you don't enable **Filter Learners for Mentors**, then mentors can see all the students in the course and access all students' work, even those for whom they are not a mentor.
 
+.. note:: If you don't enable Filter Learners for Mentors, then mentors can see all the students in the course and access all students' work, even those for whom they are not a mentor.
+
+
+
+**In Canvas:**
+
+After you have enabled Filter Learners for Mentors in your course's LTI/LMS settings, then go to Canvas and complete the following:
+
+1. In the **People** section of the course, find the mentor and click the three vertical dots on the right of the name, then click **Edit Role**.
+2. Change the role to **Observer**.
+3. Click the three vertical dots on the right of the name and click **Link to Students**.
+4. Find and click the names of the students associated with that mentor. Once done, click **Update**.
 
 .. _Destination_Page: