[TF-M] [RFC] The code review guideline

Hi,

We are creating one document to describe the code review guidelines:

https://review.trustedfirmware.org/c/TF-M/trusted-firmware-m/+/5372

The goal of this document is to introduce the source management level concepts to be followed while reviewing a code – which try to simplify the contribution (but burdens the reviewers? 😉).

Difference to the `coding style`:

* It focuses more on the source placement, interface definition and including, etc.

As this document is keeping evolving in a period, the plan is we merge a simple version as start and adding more contents by new patches, so please give enough comments if you have, and don’t forget the concept: we want to make things rational and simple.

Thanks.

/Ken