Add instructor docs for self registration

Author: IDzyre

_docs/instructor/course_management/managing_enrollment.md

@@ -40,7 +40,20 @@ traditionally registered, to immediately add a student who registered
 late, or if the feed is not available for your course.
 
 
+### Self Registration
+Submitty allows users to register for courses where specified by the Course Settings. ***This allows any user who has access to Submitty to register.*** 
 
+Currently the only option for self registration allows any users to automatically join the course upon registering. In the future, we will add a
+self-registration mode where the user requests to join the course. The instructor(s) will be able to allow or deny users from joining the course. 
+
+Once the user registers for the course, the instructor(s) will receive an email with the user's user_id and the course they registered for. 
+
+#### Enable Self Registration
+**Before you enable Self Registration, you must have at least one registration section.**
+1. Navigate to the `Course Settings` page.
+2. Scroll all the way down to the `Danger Zone`
+3. Check the checkbox for `Enable Self Registration`.
+4. (Optional) Select the default section you want users to be added to. This defaults to the first section. This can also be edited in the `Manage Sections` page.
 
 ### Add students one-at-a-time