Update CONTRIBUTION.md with pre-commit + black-primer instructions (#1459)

* Update CONTRIBUTION with pre-commit + black-primer instructions
- Inform people how to run primer and alter it's config
- Link to main documentation

* Apply suggestions from code review

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 91e5320e2830321f347c6f56200336a1b3a9ce6a..525cb9c183d3979447a09145ff24736212d0e93e 100644 (file)
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -24,7 +24,7 @@ You can use any operating system. I am using macOS myself and CentOS at work.
 
 Install all development dependencies using:
 
-```
+```console
 $ pipenv install --dev
 $ pipenv shell
 $ pre-commit install
@@ -34,12 +34,26 @@ If you haven't used `pipenv` before but are comfortable with virtualenvs, just r
 `pip install pipenv` in the virtualenv you're already using and invoke the command above
 from the cloned _Black_ repo. It will do the correct thing.
 
-Before submitting pull requests, run tests with:
+Before submitting pull requests, run lints and tests with:
 
-```
+```console
+$ pre-commit run -a
 $ python -m unittest
+$ black-primer [-k -w /tmp/black_test_repos]
 ```
 
+## black-primer
+
+`black-primer` is used by CI to pull down well-known _Black_ formatted projects and see
+if we get soure code changes. It will error on formatting changes or errors. Please run
+before pushing your PR to see if you get the actions you would expect from _Black_ with
+your PR. You may need to change
+[primer.json](https://github.com/psf/black/blob/master/src/black_primer/primer.json)
+configuration for it to pass.
+
+For more `black-primer` information visit the
+[documentation](https://github.com/psf/black/blob/master/docs/black_primer.md).
+
 ## Hygiene
 
 If you're fixing a bug, add a test. Run it first to confirm it fails, then fix the bug,