Unhardcode nova database connection parameters

[database]/[api_database]
idle_timeout = 180
min_pool_size = 100
max_pool_size = 700
max_overflow = 100
retry_interval = 5
max_retries = -1
db_max_retries = 3
db_retry_interval = 1
connection_debug = 10
pool_timeout = 120

Change-Id: I4bfa9ea7fdd1b91c0b43300df49ba79897bc7392
Related-Prod: PROD-26294
diff --git a/README.rst b/README.rst
index 90f2a4b..51ed2d1 100644
--- a/README.rst
+++ b/README.rst
@@ -1182,6 +1182,27 @@
 You can read more about it here:
     https://docs.openstack.org/security-guide/databases/database-access-control.html
 
+Nova database connection setup:
+========
+
+.. code-block:: yaml
+
+   nova:
+     controller:
+     enabled: True
+     ...
+     database:
+       idle_timeout: 180
+       min_pool_size: 100
+       max_pool_size: 700
+       max_overflow: 100
+       retry_interval: 5
+       max_retries: '-1'
+       db_max_retries: 3
+       db_retry_interval: 1
+       connection_debug: 10
+       pool_timeout: 120
+
 Upgrades
 ========