[doc] Complete doc requirements
[doc] Complete doc requirements

Currently readthedocs is unable to build the documentation because not all the
dependencies gets installed.

This patch add the wsme requirements to the doc requirements, with the hope
it fixes the build on readthedocs.

Change-Id: Ib17d3e77ec1eb0d200a0c478663c7cbd2710aed3

stackforge/wsme