repo: Add manifest file

As part of Issue#11, it was found that the requirements files were not
being bundled with any source distribution of cloudvision
Unsure how this has not been an issue prior, but adding a manifest file
to ensure that these files are added into the source distribution.
A new `post-3` version of 1.5.0 has been released on pypi to address this
problem

Change-Id: Ia16b0baf621aa80ccdd175b89a8f5ee95bae90e2

MANIFEST.in

@@ -0,0 +1 @@
+include *.txt