Added ReadTheDocs Link to README

It was difficult finding the documentation from the docs build status badge, added a heading for it.

Author: darshkpatel

README.md

@@ -30,6 +30,10 @@ This system allows the users to drag and drop Arduino components from the left p
 
 ![Arduino Demo](demo/demo-arduino.gif)
 
+## Documentation 
+
+The latest version of documentation for the project is maintained on [esim-cloud.readthedocs.io](https://esim-cloud.readthedocs.io/)
+
 ## Installation
 
 ### Basic Setup