Update docstring for GPG._sign_file().

src/gnupg.py

@@ -743,7 +743,15 @@ use_agent: %s
 
     def _sign_file(self, file, keyid=None, passphrase=None, clearsign=True,
                    detach=False, binary=False):
-        """Create a signature for a  file."""
+        """Create a signature for a file.
+
+        :param file: The file stream (i.e. it's already been open()'d) to sign.
+        :param str keyid: The key to sign with.
+        :param str passphrase: The passphrase to pipe to stdin.
+        :param bool clearsign: If True, create a cleartext signature.
+        :param bool detach: If True, create a detached signature.
+        :param bool binary: If True, do not ascii armour the output.
+        """
         log.debug("_sign_file():")
         if binary:
             log.info("Creating binary signature for file %s" % file)