Add another missing function doc

src/or/relay.c

@@ -858,7 +858,11 @@ remap_event_helper(entry_connection_t *conn, const tor_addr_t *new_addr)
                               REMAP_STREAM_SOURCE_EXIT);
 }
 
-/**DOCDOC*/
+/** Extract the contents of a connected cell in <b>cell</b>, whose relay
+ * header has already been parsed into <b>rh</b>. On success, set
+ * <b>addr_out</b> to the address we're connected to, and <b>ttl_out</b> to
+ * the ttl of that address, in seconds, and return 0.  On failure, return
+ * -1. */
 int
 connected_cell_parse(const relay_header_t *rh, const cell_t *cell,
                      tor_addr_t *addr_out, int *ttl_out)