Accessibility checks: Phase 2 - Adding Pa11y CI PR stage (#38556)

Co-authored-by: Hugo Häggmark <hugo.haggmark@grafana.com>

contribute/create-pull-request.md

@@ -55,6 +55,17 @@ Pull requests that create new UI components or modify existing ones must adhere
 - Use the [Grafana theme palette](/contribute/style-guides/themes.md) for styling. It contains colors with good contrast which aids accessibility.
 - Use [RTL](https://testing-library.com/docs/dom-testing-library/api-accessibility/) for writing unit tests. It helps to create accessible components.
 
+Pull requests that introduce accessibility(a11y) errors:
+
+We use [pa11y-ci](https://github.com/pa11y/pa11y-ci) to collect accessibility errors on [some URLs on the project](https://github.com/grafana/grafana/issues/36555), threshold errors are specified per URL.
+
+If the contribution introduces new a11y errors, our continuous integration will fail, preventing you to merge on the main branch. In those cases there are two alternatives for moving forward:
+
+- Check the error log on the pipeline step `test-a11y-frontend-pr`, identify what was the error, and fix it.
+- Locally run the command `yarn test:accessibility-report` that generates an HTML accessibility report, then go to the URL that contains your change, identify the error, and fix it. Keep in mind, a local Grafana instance needs to be running on `http://localhost:3000`.
+
+You can also prevent introducing a11y errors by installing an a11y plugin in your browser, for example, axe DevTools, Accessibility Insights for Web among others.
+
 ### Backend-specific guidelines
 
 Please refer to the [backend style guidelines](/contribute/style-guides/backend.md).