chore: update readme with action usages

Author: helenff

README.md

@@ -1 +1,72 @@
 # job-notification
+
+[![Test](https://github.com/scribd/job-notification/actions/workflows/test.yml/badge.svg?branch=main&event=push)](https://github.com/scribd/job-notification/actions/workflows/test.yml)
+
+A GitHub Action for sending job notifications
+
+## Table of contents
+
+- [Quick Start](#quick-start)
+- [Advanced usage](#advanced-usage)
+  - [Customize message](#customize-message)
+  - [Overwrite repository link](#overwrite-repository-link)
+- [Development](#development)
+  - [Testing](#testing)
+- [Maintainers](#maintainers)
+
+## Quick Start
+
+```yaml
+steps:
+  - name: Send notification 
+    if: always() # Always send notification regardless of the job status.
+    uses: scribd/job-notification@main
+    with:
+      token: ${{ secrets.SCRIBD_SLACK_GENERIC_TOKEN }}
+      channel: test-release-notification
+```
+
+## Advanced usage
+
+### Customize message
+
+By default, the notification uses the latest commit message. You can overwrite that using the `message` field. 
+
+To test the message formating, use the [Block Kit Builder](https://app.slack.com/block-kit-builder/).
+
+```yaml
+steps:
+  - name: Send notification 
+    if: always()
+    uses: scribd/job-notification@main
+    with:
+      token: ${{ secrets.SCRIBD_SLACK_GENERIC_TOKEN }}
+      channel: test-release-notification
+      message: <https://github.com/${{ github.repository }}|Released update>
+```
+
+### Overwrite repository link
+
+By default, the notification links to the repository that triggers the job. You can overwrite that using the `repository` field, which is useful for managing the release for multiple repositories in one place. See [scribd-api-proto](https://github.com/scribd/scribd-api-proto) for example.
+
+```yaml
+# Example: release.yml in scribd-api-proto
+steps:
+  - name: Send notification 
+    if: always()
+    uses: scribd/job-notification@main
+    with:
+      token: ${{ secrets.SCRIBD_SLACK_GENERIC_TOKEN }}
+      channel: test-release-notification
+      repository: scribd/scribd-api-ruby
+```
+
+## Development
+
+### Testing
+
+You can test your changes by pushing them to a branch, which will trigger the [test](.github/workflows/test.yml) workflow to send the notifications to the [test-release-notification](https://scribd.slack.com/archives/C04U68KR6CU) channel on Slack.
+
+## Maintainers
+
+Made with ❤️ by the Service Foundations teams.