Display README file for deployed Function

User story:

As a developer

I want to produce documented and transparent code

so that my end users and colleagues can understand what is going on.

Current state

For deployed Cognite Function we see three tabs: Calls, Schedules, and Details. Documentation is limited to the description field.

Desired state

I would like to see four tabs: Calls, Schedules, Details, and Documentation/Readme

I would like to be able to write a README markdown file that I package together with the handler, requirements and all the rest. This should be picked up and rendered in a dedicated tab for the function. 

I think this would really increase transparency in the deployed functions. All employees have access to CDF, but not all have access to source code repositories where documentation usually lives. The deployed Function is a black box at the moment.