Adding check (in datastore) that setup.py README is valid RST. (#3316)

Author: dhermes

packages/google-cloud-datastore/nox.py

@@ -101,6 +101,15 @@ def lint(session):
     session.run('flake8', 'google/cloud/datastore')
 
 
+@nox.session
+def lint_setup_py(session):
+    """Verify that setup.py is valid (including RST check)."""
+    session.interpreter = 'python3.6'
+    session.install('docutils', 'Pygments')
+    session.run(
+        'python', 'setup.py', 'check', '--restructuredtext', '--strict')
+
+
 @nox.session
 def cover(session):
     """Run the final coverage report.