[Documentation:System] Docs for Self Registration Courses (#637)

This PR adds documentation for
Submitty/Submitty#10778, which adds the ability
for users to register for courses if the instructor enables it in the
Course Settings page.

Author: IDzyre

_docs/instructor/course_management/managing_enrollment.md

@@ -40,7 +40,19 @@ 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
 

_docs/student/account/index.md

@@ -35,6 +35,11 @@ If you don't see a specific course on the list, contact the instructor
 or teaching staff for the course or system administrator for your
 school or department.
 
+Some courses may be 'Available for Self Registration'. These courses you can register
+for without the instructor adding you. To join the course, click on the button for the course,
+and in click on the button titled 'Register'. This will alert the instructor that you have joined the course.
+They can still remove you from the course, however they don't have to add you. 
+
 
 
 ## My Profile