Formally describe the supported documentation build process. Fixes #354.

docs/developer-guide.txt

@@ -109,3 +109,20 @@ Setuptools follows ``semver`` with some exceptions:
 - Omits 'v' prefix for tags.
 
 .. explain value of reflecting meaning in versions.
+
+----------------------
+Building Documentation
+----------------------
+
+Setuptools relies on the Sphinx system for building documentation and in
+particular the ``build_sphinx`` distutils command. To build the
+documentation, invoke::
+
+    python setup.py build_sphinx
+
+from the root of the repository. Setuptools will download a compatible
+build of Sphinx and any requisite plugins and then build the
+documentation in the build/sphinx directory.
+
+Setuptools does not support invoking the doc builder from the docs/
+directory as some tools expect.

docs/development.txt

@@ -33,4 +33,3 @@ setuptools changes.  You have been warned.
    developer-guide
    formats
    releases
-