Add a ReadTheDocs

[nathanlct]

Should we set up ReadTheDocs or I remember we mentioned something else at some point?

[eugenevinitsky]

I think @xiaomengy can set up the initial version of docusaurus and then we can build docs from there?

[nathanlct]

Since i had already started, the installation looks like:

• install Node v18 (https://github.com/nodesource/distributions/blob/master/README.md#debinstall)
• install docusaurus & build docs (https://docusaurus.io/docs/installation)

  npx create-docusaurus@latest nocturne_docs facebook  # create default docs
  cd nocturne_docs
  npm run build  # build static website in nocturne_docs/build

• deploy to github pages (https://docusaurus.io/docs/deployment#deploying-to-github-pages) <- this requires access to the "settings" tab on the github

From there we should all be able to add docs to the nocturne_docs and Travis should build/deploy automatically to github pages.