Proposal to standardize the structure of Dapr SDK contributing guidance

@marcduiker and I discussed the experience for new users and contributors of Dapr. One of the observations is that currently the contents of Readme files in SDK repos is not uniform, which means their experience can vary depending on where they land. The image shows a table with Dapr repos in columns and Readme contents in rows below.

The proposal part of this issue is open for discussion :-)

The readme files of the SDK repos differ: they reference a #contributing section, the contributing file, a docs page, or don't mention contributing. What should it be?

The contributing.md seems to be standardized (except for docs and community repos that we also looked at). Is that still ok? It is missing in the js-sdk repo, where it probably should be added.