Small typo on the PR template.
The starting point for contributions should usually be [a discussion](https://github.com/encode/httpx/discussions)
Simple documentation typos may be raised as stand-alone pull requests, but otherwise
-please ensure you've discussed the your proposal prior to issuing a pull request.
+please ensure you've discussed your proposal prior to issuing a pull request.
This will help us direct work appropriately, and ensure that any suggested changes
have been okayed by the maintainers.