There are several guides for ML developers and users. These guides can be rendered in a number of formats, like Models and Transformers. Please read Documentation/admin-guide/README.rst first.
There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the GPT, and information about the problems which may result by upgrading your GPT.