Update readme

Update the readme to provide an overall description of
the project, and also a brief description of using the API.

Change-Id: I53204798569af29d63dda84fa9d344772b36a53f

README.rst

@@ -2,6 +2,23 @@
 Kolla-CLI
 ========
 
+The Kolla-CLI project provides the ability to more easily manage
+Kolla-Ansible deployments. It provides both a CLI and a python
+API that you can use to configure and deploy OpenStack using Kolla-Ansible.
+
+Kolla-Ansible requires that hosts, groups, and services are specified
+in an inventory file. With Kolla-CLI, you can add/remove hosts, change group
+associations, etc from the CLI or API. Kolla-Ansible also maintains
+passwords and various configuration variables in a variety of global, group
+and host files. With Kolla-CLI, you can now view and change these from the
+CLI/API.
+
+Finally, Kolla-CLI provides commands to setup the SSH keys on hosts, run
+deployments and perform upgrades.
+
+Installing
+==========
+
 The following steps can be used to build / run the kolla-cli
 
 * install ansible and docker
@@ -33,7 +50,23 @@ _("message")) make sure to re-generate the i18n files with the
 >python setup.py extract_messages command and check in the files
 generated in openstack-kollacli.
 
-===============
+
+API
+===
+
+To use the API, import the ClientAPI into your module:
+
+from kolla_cli.api.client import ClientApi
+
+Then define a global:
+
+CLIENT = ClientApi()
+
+And then you can use that global to execute API commands, for example,
+to add a host to the inventory:
+
+CLIENT.host_add(['host_name'])
+
 Troubleshooting
 ===============