Added code quality checks to contributing.md (#121)

docs/contributing.md

@@ -15,6 +15,35 @@ You generally only need to submit a CLA once, so if you've already submitted one
 (even if it was for a different project), you probably don't need to do it
 again.
 
+## Code Quality Checks
+
+All notebooks in this project are checked for formatting and style, to ensure a
+consistent experience. To test notebooks prior to submitting a pull request,
+you can follow these steps.
+
+From a command-line terminal (e.g. from Vertex Workbench or locally), install
+the code analysis tools:
+```shell
+pip install -U nbqa black flake8 isort pyupgrade git+https://github.com/tensorflow/docs
+```
+
+Then, set an environment variable for your notebook (or directory):
+```shell
+export notebook="your-notebook.ipynb"
+```
+
+Finally, run this code block to check for errors. Each step will attempt to
+automatically fix any issues. If the fixes can't be performed automatically,
+then you will need to manually address them before submitting your PR.
+```shell
+nbqa black "$notebook"
+nbqa pyupgrade "$notebook"
+nbqa isort "$notebook"
+python3 -m tensorflow_docs.tools.nbfmt --remove_outputs "$notebook"
+nbqa flake8 "$notebook" --extend-ignore=W391,E501,F821,E402,F404,W503,E203,E722,W293,W291
+```
+
+
 ## Code Reviews
 
 All submissions, including submissions by project members, require review. We