Host docs on github pages

[UebelAndre]

I think it'd be helpful to host rendered stardoc docs on a github pages site similar to the following:

• https://bazelbuild.github.io/rules_rust/
• https://bazelbuild.github.io/rules_nodejs/
• https://bazelbuild.github.io/rules_foreign_cc/

Any admin of the project can set it up in just a few clicks since the docs are already committed to the repo.