Fix misspelling in the "README.rst"

Change the description to
1."- Tempest should be self-testing."
2."The etc/tempest.conf.sample attempts to be a
 self-documenting version of the configuration."
3."However, because large parts of Tempest
  are self-verifying there might be uncaught
  issues running on Python 3.4"

Closes-Bug: #1486904

Change-Id: Ic5a5446f62a3bfa7befb5ca9acbb577446faaba4
1 file changed