Add notification settings documentation and update screenshot

CHANGELOG

@@ -45,6 +45,7 @@ v 8.9.0 (unreleased)
   - Remove 'main language' feature
   - Pipelines can be canceled only when there are running builds
   - Use downcased path to container repository as this is expected path by Docker
+  - Custom notification level for projects
   - Projects pending deletion will render a 404 page
   - Measure queue duration between gitlab-workhorse and Rails
   - Make Omniauth providers specs to not modify global configuration

doc/workflow/notifications.md

@@ -4,7 +4,7 @@ GitLab has a notification system in place to notify a user of events that are im
 
 ## Notification settings
 
-Under user profile page you can find the notification settings.
+You can find notification settings under the user profile.
 
 ![notification settings](notifications/settings.png)
 
@@ -20,6 +20,7 @@ Each of these settings have levels of notification:
 * Participating - receive notifications from related resources
 * Watch - receive notifications from projects or groups user is a member of
 * Global - notifications as set at the global settings
+* Custom - Notification is set based on events selected by the user.(Available only in project level)
 
 #### Global Settings
 
@@ -71,6 +72,7 @@ In all of the below cases, the notification will be sent to:
 
 - Watchers: users with notification level "Watch"
 - Subscribers: anyone who manually subscribed to the issue/merge request
+- Custom: Users with notification level "custom" who turned on notifications for any of the events present in the table below
 
 | Event                  | Sent to |
 |------------------------|---------|