Document the different preferences that need to be set to get push notifs as expected

[abhijeetviswa]

Users may go change the notification settings willy nilly. We need to document (either within the app or the repo) the different preferences that need to be set at minimum to get notifications as expected. They are:

• In Forum Preferences, Email Digest Type needs to be set to No Digest (single email per forum post) to get notifications for every new post/discussion.
• In Notification Preferences, everything under Extended Notifications needs to be enabled (both offline and online) for each provider (phone, email, web etc) to be notified for new course modules and sections.
• In Notification Preferences, Subscribed Forum Posts under the section Forum should be enabled (both offline and online) to be notified for new forum and discussion posts. Note that this along with Email Digest Type in Forum Preferences determines if notifications are sent for each new post in a discussion.