The official devguide at https://github.com/python/devguide does not include instructions on exactly how to build the docs!  If, after cloning, you simply type `make`, you get some helpful output:

$ make
Please use `make <target>' where <target> is one of
  html       to make standalone HTML files
  dirhtml    to make HTML files named index.html in directories
  singlehtml to make a single large HTML file
  pickle     to make pickle files
  json       to make JSON files
  htmlhelp   to make HTML files and a HTML help project
  qthelp     to make HTML files and a qthelp project
  devhelp    to make HTML files and a Devhelp project
  epub       to make an epub
  latex      to make LaTeX files, you can set PAPER=a4 or PAPER=letter
  latexpdf   to make LaTeX files and run them through pdflatex
  text       to make text files
  man        to make manual pages
  changes    to make an overview of all changed/added/deprecated items
  linkcheck  to check all external links for integrity
  doctest    to run all doctests embedded in the documentation (if enabled)
  check      to run a check for frequent markup errors

However, in order to build, say, HTML, you need to have sphinx installed in your environment.  I would like to add a `requirements.txt` file that will specify which dependencies must be installed (into a virtualenv, probably), in order to successfully build the documentation.  In the GitHub PR, I have also added a BUILDING.rst that explains how to install the dependencies for building the documentation.