[docs] asset - best practices

[mercillo]

Is your feature request related to a problem? Please describe.
As more people use player; there are many ways to write your own assets. We should provide a guideline/best practices on writing assets / transforms / dsl / tests / etc.

There are many rules/guidelines that we should suggest to people.

Describe the solution you'd like
We should have basic guidelines/examples for a "ready to use" asset that people can reference and use.
A possible solution could be to create a decision tree to help people decide what functionality/files that they would need to get the asset started. Such if they need to add a transform, etc.

Additional context