Document the Response.close() method.

requests/models.py

@@ -689,4 +689,9 @@ class Response(object):
             raise HTTPError(http_error_msg, response=self)
 
     def close(self):
+        """Closes the underlying file descriptor and releases the connection
+        back to the pool.
+
+        *Note: Should not normally need to be called explicitly.*
+        """
         return self.raw.release_conn()