Merge branch 'docs-fe-accessibility' into 'master'

Add docs for frontend accessibility

See merge request gitlab-org/gitlab-ce!17624

doc/development/new_fe_guide/development/accessibility.md

-# Accessibility
+# Accessiblity
+Using semantic HTML plays a key role when it comes to accessibility.
 
-> TODO: Add content
+## Accessible Rich Internet Applications - ARIA
+WAI-ARIA, the Accessible Rich Internet Applications specification, defines a way to make Web content and Web applications more accessible to people with disabilities. 
+
+> Note: It is [recommended][using-aria] to use semantic elements as the primary method to achieve accessibility rather than adding aria attributes. Adding aria attributes should be seen as a secondary method for creating accessible elements.
+
+### Role
+The `role` attribute describes the role the element plays in the context of the document.
+
+Check the list of WAI-ARIA roles [here][roles]
+
+## Icons
+When using icons or images that aren't absolutely needed to understand the context, we should use `aria-hidden="true"`.
+
+On the other hand, if an icon is crucial to understand the context we should do one of the following:
+1. Use `aria-label` in the element with a meaningful description
+1. Use `aria-labelledby` to point to an element that contains the explanation for that icon
+
+## Form inputs
+In forms we should use the `for` attribute in the label statement:
+```
+<div>
+  <label for="name">Fill in your name:</label>
+  <input type="text" id="name" name="name">
+</div>
+```
+
+## Testing
+
+1. On MacOS you can use [VoiceOver][voice-over] by pressing `cmd+F5`.
+1. On Windows you can use [Narrator][narrator] by pressing Windows logo key + Ctrl + Enter.
+
+## Online resources
+
+- [Chrome Accessibility Developer Tools][dev-tools] for testing accessibility
+- [Audit Rules Page][audit-rules] for best practices
+- [Lighthouse Accessibility Score][lighthouse] for accessibility audits
+
+[using-aria]: https://www.w3.org/TR/using-aria/#notes2
+[dev-tools]: https://github.com/GoogleChrome/accessibility-developer-tools
+[audit-rules]: https://github.com/GoogleChrome/accessibility-developer-tools/wiki/Audit-Rules
+[aria-w3c]: https://www.w3.org/TR/wai-aria-1.1/
+[roles]: https://www.w3.org/TR/wai-aria-1.1/#landmark_roles
+[voice-over]: https://www.apple.com/accessibility/mac/vision/
+[narrator]: https://www.microsoft.com/en-us/accessibility/windows
+[lighthouse]: https://developers.google.com/web/tools/lighthouse/scoring#a11y