flesh out readme

Author: tedivm

README.md

@@ -1 +1,46 @@
 # Python Versionator - Github Action
+
+This Github Action is part of the [Multi-Py Project](https://github.com/multi-py). It works alongside the [Multi-Py Image Builder Action](https://github.com/multi-py/action-python-image-builder) to continuously release multiarchitecture containers.
+
+The Versionator takes three primary actions-
+
+* Updates a designated workflow with the most recent versions of a Python package.
+* Updates that same workflow with the most recent Python versions.
+* Updates the project README file based off of the templates in this project.
+
+In other words, when a Python package gets pushed to PyPI this action will update workflows to use it. This is how Multi-Py can release new containers quickly after upstream packages are released.
+
+## Example Workflow
+
+```yaml
+# Every 30 minutes check for a new version of the package.
+on:
+  push:
+    branches:
+      - 'main'
+  schedule:
+    - cron:  '0,30 * * * *'
+
+jobs:
+  Version-Updater:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+        with:
+          # Github Actions can't be granted the required workflow
+          # permissions, so it has to be a Personal Access Token.
+          token: ${{ secrets.WORKFLOW_GITHUB_TOKEN }}
+
+      - name: "Update Build Workflow"
+        uses: multi-py/action-python-versionator@main
+        with:
+          package: "uvicorn"
+          git_name: "Robert Hafner"
+          git_email: "user@example.com"
+          action_path: ${{ github.workspace }}/.github/workflows/build_and_push.yml
+```
+
+## Readme Templates
+
+The default templates are very specific to the Multi-Py project. Templates can be overridden- by default any files in your repo's `templates` directory will get used instead of the action ones. A `README.md` file will replace the entire default template, or specific components can be overridden while allowing the others to remain (`description.md`, `quick_start.md`, `tags.md`, `documentation.md`). The `template_directory` parameter can be used to specific a different template directory.