Use Apps readme file to detail changelog & API specifications

Lets use the `README.md` file in our apps to document things such as changes log & JSON structure for the different APIs that app uses. This helps new developers on the project to easily jump in and be able to see the different API. This helps with setting up new features that requires date change in both the API and Mirage. I am proposing this to be part of the definition of done for the UI team.