Merge branch 'docs-issue-board-focus-mode' into 'master'

Issue board focus mode docs

See merge request !1618

doc/user/project/issue_board.md

@@ -200,6 +200,12 @@ milestone with the due date that is next.
 
 ![Update boards milestone](img/issue_board_multiple_milestone.png)
 
+## Focus mode
+
+Click the button at the top right to toggle focus mode on and off. In focus mode, the navigation UI is hidden, allowing you to focus on issues in the board.
+
+![Board focus mode](img/issue_board_focus_mode.gif)
+
 ## Permissions
 
 [Developers and up](../permissions.md) can use all the functionality of the