flesh out readme

Author: tedivm

README.md

@@ -1 +1,55 @@
 # Python Image Builder - Github Action
+
+This Github Action is part of the [Multi-Py Project](https://github.com/multi-py). It works alongside the [Multi-Py Python Versionator Action](https://github.com/multi-py/action-python-versionator) to continuously release multiarchitecture containers.
+
+The Image Builder is focused on building a single multiarchitecture image around a python package. It uses a two stage approach where the python packages are compiled in a base image and then moved to the final image. This allows for consistent builds and smaller output images.
+
+Using this action, the Github Action Matrix Strategy, and the Versionator allows for building a complex set of images with the most recent versions of the tracked packages.
+
+## Example
+
+```yaml
+
+name: Example Image Builder
+
+# Publish on new pushed, and build on Monday Morning (UTC) regardless.
+on:
+  push:
+    branches:
+      - 'main'
+  schedule:
+    - cron:  '4 0 * * MON'
+
+jobs:
+  Uvicorn-Builder:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        python_version: ["3.6", "3.7", "3.8", "3.9", "3.10"]
+        package_versions: ["0.12.1", "0.12.2", "0.12.3", "0.13.0", "0.13.1", "0.13.2", "0.13.3", "0.13.4", "0.14.0", "0.15.0"]
+        target_base: ["full", "slim", "alpine"]
+    steps:
+
+      - name: Checkout repository
+        uses: actions/checkout@v2
+
+      - name: "Create and push"
+        uses: multi-py/action-python-image-builder@main
+        with:
+          package: "uvicorn"
+          package_latest_version: "0.15.0"
+          maintainer: "Myname <[email protected]>"
+          python_version: ${{ matrix.python_version }}
+          target_base: ${{ matrix.target_base }}
+          package_version: ${{ matrix.package_versions }}
+          registry_password: ${{ secrets.GITHUB_TOKEN }}
+```
+
+The `python_version`, `package_versions`, and `package_latest_version` values get updated by a separate Versionator action.
+
+This particular config supports five python versions, three variant images, ten package versions, and three architectures. This results in 150 high level images each consisting of three architectures, for a total of 450 builds across 150 workflows on each run.
+
+## Docker Files and Context
+
+By default this action uses its own dockerfile and repository as context. This can be overridden with the `dockerfile` and `docker_build_path` parameters. To get the most out of this action start with the dockerfile here and expand it so that build arguments will still work.