Add blurb to CONTRIBUTING.md about regression env vars
@@ -90,6 +90,7 @@ Running tests locally
Our tests are managed by `tox`, which runs both `pytest` and our system of makefiles.
This exercises the contents of both the `tests` and `examples` directories.
+`tox` supports the usage of the environment variables `SIM` and `TOPLEVEL_LANG` to direct how to run the regression.
Managing of Issues and Pull Requests
