Update CONTRIBUTING.md (#2855)

* Update CONTRIBUTING.md

Added docker option to testing section.

* Apply suggestions from code review

Co-authored-by: Jirka Borovec <Borda@users.noreply.github.com>

.github/CONTRIBUTING.md

@@ -174,7 +174,7 @@ _Artifacts_ tab in CircleCI when you click on the task named _ci/circleci: Build
 
 ### Testing
 
-Testing your work locally will help you speed up the process since it allows you to focus on particular (failing) test-cases.
+**Local:** Testing your work locally will help you speed up the process since it allows you to focus on particular (failing) test-cases.
 To setup a local development environment, install both local and test dependencies:
 
 ```bash
@@ -190,9 +190,13 @@ bash .run_local_tests.sh
 
 Note: if your computer does not have multi-GPU nor TPU these tests are skipped.
 
-For convenience, you can also use your own CircleCI building which will be triggered with each commit.
+**GitHub Actions:** For convenience, you can also use your own GHActions building which will be triggered with each commit.
 This is useful if you do not test against all required dependency versions.
-To do so, login to [CircleCI](https://app.circleci.com/) and enable your forked project in the dashboard. It will just work after that.
+
+**Docker:** Another option is utilize the [pytorch lightning cuda base docker image](https://hub.docker.com/repository/docker/pytorchlightning/pytorch_lightning/tags?page=1&name=cuda). You can then run:
+```bash
+python -m pytest pytorch_lightning tests pl_examples -v --flake8
+```
 
 ### Pull Request