commands: add note about import retrieving patches from URLs

mercurial/commands.py

@@ -1729,7 +1729,8 b' def import_(ui, repo, patch1, *patches, '
     With -s/--similarity, hg will attempt to discover renames and
     copies in the patch in the same way as 'addremove'.
 
-    To read a patch from standard input, use "-" as the patch name.
+    To read a patch from standard input, use "-" as the patch name. If
+    a URL is specified, the patch will be downloaded from it.
     See 'hg help dates' for a list of formats valid for -d/--date.
     """
     patches = (patch1,) + patches