Update docs build commands

[pkerpedjiev]

Description

Small PR to update the docs build reference commands.

Why is it necessary?

I look at these commands whenever I rebuild the docs in the higlass-docs-dev and higlass-docs repos. Because the current procedure is to push the docs subtree to each of those repositories, the reference commands need to be up-to-date here.

This is like meta-documentation. Documentation about how to build the documentation.

Checklist

• Unit tests added or updated
• Documentation added or updated
• Example added or updated
• Screenshot for visual changes (e.g. new tracks)
• Updated CHANGELOG.md

[flekschas]

Awesome stuff