Improve docstring

Author: humitos

readthedocs/projects/models.py

@@ -653,7 +653,7 @@ def vcs_repo(self, version=LATEST, environment=None):
 
     def repo_nonblockinglock(self, version, max_lock_age=None):
         """
-        Return a ``NonBlockingLock`` or raise an exception.
+        Return a ``NonBlockingLock`` to acquire the lock via context manager.
 
         :param version: project's version that want to get the lock for.
         :param max_lock_age: time (in seconds) to consider the lock's age is old