Add reasoning for all Conventions.

[Jshewmaker]

I was looking through Very Good Engineering Conventions and saw Opinionated “Recommended” Practices for flutter_bloc.

I thought there was some good reading on the repo, but I didn't see any reasoning for why we should trust those practices. The Github user is not someone I would assume most people are familiar with and we don't provide any reasoning for why we agree with their opinions.

I think adding a line for why we agree with their reasoning or who they are would be useful in providing credibility to the link.