Update tox.ini for sphinx build instructions.

Earlier we specified, that we must generate sample config
file before generating docs. Now after commit 13ed69f
got merged, we must update the comments or any info related
to generating config file.

Change-Id: Ic0686322f07045700ff390eea8faa05eebe3df7c

tox.ini

@@ -108,7 +108,6 @@ commands =
 commands = {posargs}
 
 [testenv:docs]
-# The sample config file we generate is included in the sphinxdoc, so build that first.
 commands =
    python setup.py build_sphinx {posargs}