Watcher official install-guide

Currently watcher project does not have an official
install guide at [1]

This patch adds watcher install guide for rdo and debian.

install-guide is written following the document [2].

[1] https://docs.openstack.org/project-install-guide/ocata/
[2] https://docs.openstack.org/contributor-guide/project-install-guide.html

Change-Id: Idfae7286003f81222dadf91ddcaf95a42c7eb07f

test-requirements.txt

@@ -15,10 +15,12 @@ testscenarios>=0.4 # Apache-2.0/BSD
 testtools>=1.4.0 # MIT
 
 # Doc requirements
+openstackdocstheme>=1.5.0  # Apache-2.0
 oslosphinx>=4.7.0 # Apache-2.0
 sphinx!=1.6.1,>=1.5.1 # BSD
 sphinxcontrib-pecanwsme>=0.8 # Apache-2.0
 
+
 # releasenotes
 reno>=1.8.0 # Apache-2.0