README.md formatting fix

Author: nhooyr

README.md

@@ -37,7 +37,7 @@ See GitHub issues for minor issues but the major future enhancements are:
 - [ ] Ping pong instrumentation callbacks [#246](https://github.com/nhooyr/websocket/issues/246)
 - [ ] Graceful shutdown helpers [#209](https://github.com/nhooyr/websocket/issues/209)
 - [ ] Assembly for WebSocket masking [#16](https://github.com/nhooyr/websocket/issues/16)
-      - WIP at [#326](https://github.com/nhooyr/websocket/pull/326), about 3x faster
+  - WIP at [#326](https://github.com/nhooyr/websocket/pull/326), about 3x faster
 - [ ] HTTP/2 [#4](https://github.com/nhooyr/websocket/issues/4)
 - [ ] The holy grail [#402](https://github.com/nhooyr/websocket/issues/402)