Add README for github workflows directory

.github/workflows/README.md

@@ -0,0 +1,24 @@
+This directory contains GitHub Actions (GHA) yaml files as well as helper files they use.
+
+## Building and pushing Docker images
+
+* Each workflow `docker_{module name}.yml` is used to build the given module's Docker image.
+* `docker_all-modules.yml` builds and pushes all module Docker images by calling each `docker_{module name}.yml` workflow.
+* The `build-push-docker-module.yml` workflow is not standlone but contains actions used by `docker_all-modules.yml` and each `docker_{module name}.yml`.
+
+## Module testing
+
+* Each workflow `run_{module name}.yml` is used to run the given module in CI using the test data.
+* `run_all-modules.yml` runs all modules in CI by calling each `run_{module name}.yml` workflow.
+
+## Creating releases
+
+* `file-periodic-release-issues.yml` files issues to prepare for a periodic (dated) release.
+* `create-periodic-release.yml` creates a periodic (dated) release.
+
+## Repository maintenance
+
+* `spellcheck.yml` performs spell checking of markdown and R Markdown documents.
+* `code-styling.yml` performs code styling using `styler` and `ruff`.
+  * This workflow also consumes `modules_code-styling.txt` to determine which modules to style.
+  When modules reach the development stage where they should be automatically styled, they should be added to this text file.