[Enhancement] - Add OpenSearch description document to documentation

[khalidabuhakmeh]

Adding an OpenSearch description document to the documentation site allows developers to search our docs directly from supporting web browsers. Meaning they can go straight to search without first navigating to our docs home page. That's pretty cool.

[maartenba]

Does look slightly involved (needs a suggestions endpoint it seems, which I assume would be server side?)

[khalidabuhakmeh]

The other issue might be that you need a server to return the specific content type of application/opensearchdescription+xml. So this is more of a server limitation than just returning an XML file. :\