Create a docset for Dash or similiar tools

I use Dash a lot to browse documentation locally and even offline. It makes sense to provide these for people using documentation browsing tools.

Reference: [Docset Generation Guide](https://kapeli.com/docsets)

The issue names no project files, tests, or entry points. Read the linked Docset Generation Guide first and establish the docset's required source and output; done means providing a usable offline docset for the project's documentation.

Written by the indexing model from the issue text.