now using the canonical doc

CONTRIBUTING.md

@@ -79,6 +79,26 @@ git checkout -b <branch name>
 After you make your changes, you can use the following commands to see
 what's been modified and check out the diffs:  `git status` and `git diff`.
 
+### Building the image locally
+
+You should use [repo2docker](https://repo2docker.readthedocs.io/en/latest/) to build and use/test the image on your own device before you push and create a PR.  It's better (and typically faster) to do this first before using CI/CD.  There's no need to waste Github Action minutes to test build images when you can do this on your own device!
+
+Run `repo2docker` from inside the cloned image repo.  To run on a linux/WSL2 linux shell:
+```
+repo2docker . # <--- the path to the repo
+```
+
+If you are using an ARM CPU (Apple M* silicon), you will need to run `jupyter-repo2docker` with the following arguments:
+
+```
+jupyter-repo2docker --user-id=1000 --user-name=jovyan \
+  --Repo2Docker.platform=linux/amd64 \
+  --target-repo-dir=/home/jovyan/.cache \
+  -e PLAYWRIGHT_BROWSERS_PATH=/srv/conda \
+  . # <--- the path to the repo
+```
+
+If you just want to see if the image builds, but not automatically launch the server, add `--no-run` to the arguments (before the final `.`).
 
 When you're ready to push these changes, first you'll need to stage them for a
 commit: