Merge branch 'docs-epics-keyboard-shortcuts' into 'master'

Update keyboard shortcuts docs - Epics

See merge request gitlab-org/gitlab-ee!8409

doc/workflow/shortcuts.md

@@ -83,6 +83,14 @@ You can see GitLab's keyboard shortcuts by using 'shift + ?'
 | <kbd>e</kbd> | Edit issue/merge request |
 | <kbd>l</kbd> | Change label |
 
+## Epics
+
+| Keyboard Shortcut | Description |
+| ----------------- | ----------- |
+| <kbd>r</kbd> | Reply (quoting selected text) |
+| <kbd>e</kbd> | Edit description |
+| <kbd>l</kbd> | Change label |
+
 ## Wiki pages
 
 | Keyboard Shortcut | Description |