Read the Docs is built on top of Sphinx, which has always relied on reStructuredText as an input mechanism. We have long heard from folks that they want to write documentation in Markdown, as well as RST.
Today we are announcing that this is now possible! With the standardization of Markdown into Commonmark, we have the ability to support a markup language with a proper spec. recommonmark is the bridge that allows Commonmark to be used inside Sphinx. This allows you to use both RST and Commonmark inside of your Sphinx project.