add documentation for file locks

Author: Meaghan Lewis

docs/using/images/locked-scene.png

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+# Locking files
+
+## Request locks
+
+From the Project tab, right-click on a file to open the context menu and select `Request Lock`.
+<img src="images/request-lock.png"/>
+
+## View locks
+
+After requesting a lock, a lock icon appears in the bottom right-hand corner of the file.
+<img src="images/locks-view.png"/>
+
+A list of all locked files will appear in the **Locks** view in the GitHub tab.
+<img src="images/locked-scene.png"/>
+
+## Release locks
+
+There are two ways to release locks:
+
+1. From the Project tab, right-click on the locked file to open the context menu and select the option to `Release Lock`.
+<img src="images/release-lock.png"/>
+
+2. From the GitHub tab under **Locks** view, right-click to open the context menu and select to `Release Lock`.
+<img src="images/locks-view-right-click.png"/>
+
+There are also two options for how to release a lock on a file. Always choose the `Release Lock` option first. The `Release Lock (forced)` option can be used to remove someone else's lock.