Add note from borg with-lock about copy repo (#3749)

docs: Improve FAQ about copying a repo

docs/faq.rst

@@ -27,7 +27,13 @@ Can I copy or synchronize my repo to another location?
 ------------------------------------------------------
 
 Yes, you could just copy all the files. Make sure you do that while no
-backup is running (use `borg with-lock ...`). So what you get here is this:
+backup is running. If you copy a repository while a backup is running, 
+the lock held will be present in the copy. Thus, before using borg on the copy 
+from a different host, you need to use :ref:`break-lock` on the copied 
+repository, because Borg is cautious and does not automatically remove 
+stale locks made by a different host.
+
+So what you get here is this: 
 
 - client machine ---borg create---> repo1
 - repo1 ---copy---> repo2