chore: add readme (#3)

Author: juleswritescode

README.md

@@ -0,0 +1,23 @@
+# PostgresTools GitHub Action
+
+This is a simple action that will install [PostgresTools](https://github.com/supabase-community/postgres_lsp) on your runner. It will install the appropriate binary for your machine.
+
+It has a single input: `version: latest | <semver>`.
+Use `latest` if you want to use the latest available version in your runner.
+Use a specific tag, such as `0.2.0`, if you want to use a specific version.
+
+Whatever version is used will be output as `outputs.installed-version`.
+
+## Example Usage
+
+```yaml
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: supabase-community/pglt-cli-action@1
+        with:
+          version: 0.2.0
+      - run: postgrestools check --skip-db test.sql
+```