Creates a new file TESTING.rst.

Creates a new file called TESTING.rst making the file discoverable.

Contents of the file include very generic instructions to get newcomers
started with testing. File also includes links, including the OpenStack
wiki page on testing, encouraging the curious to access greater options
for testing individual projects as well as greater flexibility in testing.

Change-Id: I57ab249133eccd38fa5302809e06172ed6a7d89e
Merge "Creates a new file TESTING.rst."