DOCSP-35386 Add an automation authentication section (#260)

* DOCSP-35386 Add an automation authentication section

* Update source/atlas-cli-automate.txt

Co-authored-by: pierwill <[email protected]>

---------

Co-authored-by: pierwill <[email protected]>

Author: kanchana-mongodb

source/atlas-cli-automate.txt

@@ -42,6 +42,16 @@ Best Practices for Automation with the {+atlas-cli+}
 Follow these best practices when you automate processes with the
 {+atlas-cli+}:
 
+Use |service| Private Keys 
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When you create a script to automate processes, we recommend that you
+use |service| :ref:`private keys <atlas-admin-api-access>` to access
+|service|. {+atlas-cli+} login sessions last for twelve hours,
+after which you must login again to access |service|. Use |service|
+:ref:`private keys <atlas-admin-api-access>` for continued access to
+|service|. 
+
 Base Your Script on the Version of the {+atlas-cli+} that You Run
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~