Add centos 8 repository info

The tripleo repos rpm to be installed has changed its python version
and its path - now residing under components/tripleo and needs its
location updated.

Change-Id: Ifd671623b053789a99ce1e4c49c994e8e4d07241

_custom/custom.css

@@ -64,6 +64,8 @@
 
 /* tags */
 .fedora28 {background: #aee;}
+.centos7 {background: #cea;}
+.centos8 {background: #cae;}
 .rhel {background: #fee;}
 .portal {background-color: #ded;}
 .satellite {background-color: #dee;}

deploy-guide/source/repositories.rst

@@ -5,13 +5,26 @@
    and commands appearing below should not be taken as indication that this
    is fully supported by TripleO - we're still working on it!
 
-#. Download and install the python2-tripleo-repos RPM from
-   `the current RDO repository <https://trunk.rdoproject.org/centos7/current/>`_.
-   For example
+#. Download and install the python-tripleo-repos RPM from
+   the appropriate RDO repository
 
-   .. code-block:: bash
+   .. admonition:: CentOS 7
+      :class: centos7
+
+      Current `Centos 7 RDO repository <https://trunk.rdoproject.org/centos7/current/>`_
+
+       .. code-block:: bash
+
+          sudo yum install -y https://trunk.rdoproject.org/centos7/current/python2-tripleo-repos-<version>.el7.centos.noarch.rpm
+
+   .. admonition:: CentOS 8
+      :class: centos8
+
+      Current `Centos 8 RDO repository <https://trunk.rdoproject.org/centos8/component/tripleo/current/>`_.
+
+       .. code-block:: bash
 
-      sudo yum install -y https://trunk.rdoproject.org/centos7/current/python2-tripleo-repos-<version>.el7.centos.noarch.rpm
+          sudo dnf install -y https://trunk.rdoproject.org/centos8/component/tripleo/current/python3-tripleo-repos-<version>.el8.noarch.rpm
 
    .. note::