Updated pre-commit section of setup docs to be a bit more helpful

docs/source/confluence/dockerized-setup.rst

@@ -32,12 +32,33 @@ Note: If you notice 'no such file or directory' errors with the docker compose c
 3. Run ``make reallyclean``
 4. Run ``make build`` again, followed by the docker compose command previously mentioned.
 
-You'll want to set up pre-commit hooks to run automatically, so your code can be
-checked to fit with our standards. To do this:
+Set up Pre-Commit
+~~~~~~~~~~~~~~~~~
 
-1. Run `make init` which will install the `pre-commit` utility
-2. Check the installation worked with `pre-commit --version`
-3. Install the hooks defined in `.pre-commit-config.yaml` by running `pre-commit install` from the base directory
+You'll want to set up pre-commit_ to run its hooks on commit so that our standards can be enforced on your code.
+To do this:
+
+1. Run ``make init``, which will install the `pre-commit` utility
+2. Check the installation worked with ``pre-commit --version``
+3. Install the hooks defined in `.pre-commit-config.yaml` by running ``pre-commit install`` from the base directory
+4. Force the 1.1GB Docker image used by the `license-eye` hook to download by making a "toy" commit:
+
+.. code-block:: sh
+
+    touch a.py
+    git add a.py
+    git commit -m "Testing pre-commit"
+
+You should see the `license-eye` hook fail with a message about needing to fix a file.
+
+5. To clean up, run:
+
+.. code-block:: sh
+
+    git restore --staged a.py
+    rm a.py
+
+**NB:** If you get a 530 error while pulling the Docker image, *it is transient* [1_].
 
 Now the pre-commit checks should run automatically every time you commit.
 
@@ -184,3 +205,5 @@ Happy Developing!
 .. |image2| image:: media/dockerized-setup-2.png
 .. |image3| image:: media/dockerized-setup-3.png
 .. |image4| image:: media/dockerized-setup-4.png
+.. _1: https://stackoverflow.com/questions/59891901/why-do-i-suddenly-get-error-530-when-executing-docker-pull-python3-7-slim-bust
+.. _pre-commit: https://pre-commit.com