add readme

Author: lyqht

README.md

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+# GitHub action to generate Supabase Database types
+
+This GitHub action workflow aims to help you to create Supabase database definition types based on the Swagger OpenAPI specification of your Supabase REST data endpoint.
+
+## What it does
+
+This workflow is a composite action:
+
+- To generate database types based on the Swagger OpenAPI specification of your Supabase project REST data endpoint, [openapi-typescript](https://github.com/drwpow/openapi-typescript) is used.
+- Checking for file changes is done using the [get-diff-action](https://github.com/technote-space/get-diff-action).
+- Commit and push github actions to your repo are performed by the [git-auto-commit action](https://github.com/stefanzweifel/git-auto-commit-action).
+
+## How to use
+
+If you are new to GitHub Actions, refer to [this section](#if-you-dont-have-an-existing-github-action-workflow-for-your-repository). Otherwise, you can get started by referring to to the example given and the input options available.
+
+### Example
+
+```yml
+name: Update database types
+on:
+  schedule:
+    - cron: '*/60 * * * *'
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: lyqht/generate-supabase-database-types@main
+        with:
+            SUPABASE_URL: ${{secrets.SUPABASE_URL }} # e.g. https://interestingproject.supabase.co
+            SUPABASE_ANON_KEY: ${{ secrets.SUPABASE_ANON_KEY }}
+            OUTPUT_PATH: src/types/supabase.ts
+```
+
+### If you don't have an existing GitHub Action workflow for your repository
+
+1. Create a folder `.github/workflows` if you don't have it already 
+2. Inside that folder, create a YAML file say `article-badge.yml`
+3. In the `article-badge.yml` file, you can copy the example above and modify it to your usage.
+4. You can choose to declare the `schedule` with a cron expression to run the job at a specified frequency e.g. every day once.
+