add README

cloud-functions/post-deployment/README.md

+Functionality of the Cloud Function
+
+    Once Jenkin Job is  finished regardless of it's status , it will published the message (pipelines details , build number , status etc) to topic which triggers this cloud function
+    Function reads the message and make the call to jekins to get the job status pushes the data to cloud firestore and make another call to http endpoint to update the confluence with application current version
+
+# Block diagram of the Flow
+![Block Diagram](post-deployment.png?raw=true "Block Diagram")
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