mq: add a little documentation on qpush -f

hgext/mq.py

@@ -1902,7 +1902,10 b' def savename(path):'
     return newpath
 
 def push(ui, repo, patch=None, **opts):
-    """push the next patch onto the stack"""
+    """push the next patch onto the stack
+    
+    When --force is applied, all local changes in patched files will be lost.
+    """
     q = repo.mq
     mergeq = None