add github action test readme

Author: nicktrn

.github/test/README.md

@@ -0,0 +1,70 @@
+# GitHub Action Tests
+
+This directory contains necessary files to allow local testing of GitHub Actions workflows, composite actions, etc. You will need to install [act](https://github.com/nektos/act) to perform tests.
+
+## Workflow tests
+
+Trigger specific workflow files by specifying their full path:
+
+```
+act -W .github/workflow/release.yml
+```
+
+You will likely need to override any custom runners we use, e.g. buildjet. For example:
+
+```
+override=catthehacker/ubuntu:act-latest
+
+act -W .github/workflow/release.yml \
+    -P buildjet-8vcpu-ubuntu-2204=$override
+
+# override multiple images at the same time
+act -W .github/workflow/release.yml \
+    -P buildjet-8vcpu-ubuntu-2204=$override \
+    -P buildjet-16vcpu-ubuntu-2204=$override
+```
+
+Trigger with specific event payloads to test pushing to branches or tags:
+
+```
+override=catthehacker/ubuntu:act-latest
+
+# simulate push to main
+act -W .github/workflow/publish.yml \
+    -P buildjet-8vcpu-ubuntu-2204=$override \
+    -P buildjet-16vcpu-ubuntu-2204=$override \
+    -e .github/events/push-tag-main.json
+
+# simulate a `build-` prefixed tag
+act -W .github/workflow/publish.yml \
+    -P buildjet-8vcpu-ubuntu-2204=$override \
+    -P buildjet-16vcpu-ubuntu-2204=$override \
+    -e .github/events/push-tag-buld.json
+```
+
+By default, `act` will send a push event. To trigger a different event:
+
+```
+# basic syntax
+act <EVENT> ...
+
+# simulate a pull request
+act pull_request
+
+# only trigger a specific workflow
+act pull_request -W .github/workflow/pr_checks.yml
+```
+
+## Composite action tests
+
+The composite (custom) action tests can be run by triggering the `test-actions` workflow:
+
+```
+act -W .github/test/test-actions.yml
+```
+
+## Helpful flags
+
+- `--pull=false` - perform fully offline tests if all images are already present
+- `-j <job_name>` - run the specified job only
+- `-l push` - list all workflows with push triggers