Improve the UX around sample config generation

This commit just adds some documentation around using the sample config
generator. It also adds a wrapper script that sets the env variable for
running the oslo generator script with tempest.

Change-Id: I860b17defeeb85174e68b1e8b046b0e43c30683b
diff --git a/README.rst b/README.rst
index 0996022..96f6e4c 100644
--- a/README.rst
+++ b/README.rst
@@ -79,6 +79,9 @@
 document. The etc/tempest.conf.sample attempts to be a self
 documenting version of the configuration.
 
+The sample config file is auto generated using the script:
+tools/generate_sample.sh
+
 The most important pieces that are needed are the user ids, openstack
 endpoints, and basic flavors and images needed to run tests.