mount docs: apply jdchristensen's suggestion, better phrasing.

src/borg/archiver.py

@@ -3158,8 +3158,8 @@ class Archiver:
         Unmounting in these cases could cause an active rsync or similar process
         to unintentionally delete data.
 
-        When running in the foreground ^C/SIGINT unmounts cleanly, but other
-        signals or crashes do not.
+        When running in the foreground, ^C/SIGINT cleanly unmounts the filesystem,
+        but other signals or crashes do not.
         """)
 
         if parser.prog == 'borgfs':