Add documentation for Github Actions

Author: James Curtin

docs/configuration/github_action.md

@@ -0,0 +1,63 @@
+# Github Action
+
+isort provides an official [Github Action][github-action-docs] that can be used as part of a CI/CD workflow to ensure a project's imports are properly sorted.
+The action can be found on the [Github Actions Marketplace][python-isort].
+
+## Usage
+
+The `python-isort` plugin is designed to be run in combination with the [`checkout`][checkout-action] and [`setup-python`][setup-python] actions.
+By default, it will run recursively from the root of the repository being linted and will exit with an error if the code is not properly sorted.
+
+### Inputs
+
+#### `isortVersion`
+
+Optional. Version of `isort` to use. Defaults to latest version of `isort`.
+
+#### `sortPaths`
+
+Optional. List of paths to sort, relative to your project root. Defaults to `.`
+
+#### `configuration`
+
+Optional. `isort` configuration options to pass to the `isort` CLI. Defaults to `--check-only --diff`.
+
+#### `requirementsFiles`
+
+Optional. Paths to python requirements files to install before running isort.
+If multiple requirements files are provided, they should be separated by a space.
+If custom package installation is required, dependencies should be installed in a separate step before using this action.
+
+!!! tip
+    It is important that the project's dependencies be installed before running isort so that third-party libraries are properly sorted.
+
+### Outputs
+
+#### `isort-result`
+
+Output of the `isort` CLI.
+
+### Example usage
+
+```yaml
+name: Run isort
+on:
+  - push
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+        with:
+          python-version: 3.8
+      - uses: jamescurtin/isort-action@master
+        with:
+            requirementsFiles: "requirements.txt requirements-test.txt"
+```
+
+[github-action-docs]: https://docs.github.com/en/free-pro-team@latest/actions
+[python-isort]: https://github.com/marketplace/actions/python-isort
+[checkout-action]: https://github.com/actions/checkout
+[setup-python]: https://github.com/actions/setup-python