docs/rst: Use pandoc to render ReStructuredText

docs/rst: Use pandoc to render ReStructuredText

Sphinx uses ReStructuredText as its markup format.  Although missing the
project wide integration, individual *.rst files can be rendered by pandoc to
suppliement our existing ad-hoc documentation.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>