Mention break-lock in checkpointing FAQ entry (#3340)

Mention break-lock in checkpointing FAQ entry, fixes #3328

docs/faq.rst

@@ -132,10 +132,11 @@ completed is useful because it references all the transmitted chunks up
 to the checkpoint. This means that in case of an interruption, you only need to
 retransfer the data since the last checkpoint.
 
-If a backup was interrupted, you do not need to do any special considerations,
-just invoke ``borg create`` as you always do. You may use the same archive name
-as in previous attempt or a different one (e.g. if you always include the current
-datetime), it does not matter.
+If a backup was interrupted, you normally do not need to do anything special,
+just invoke ``borg create`` as you always do. If the repository is still locked,
+you may need to run ``borg break-lock`` before the next backup. You may use the 
+same archive name as in previous attempt or a different one (e.g. if you always
+include the current datetime), it does not matter.
 
 Borg always does full single-pass backups, so it will start again
 from the beginning - but it will be much faster, because some of the data was