Improve documentation about project to be able to add CII Best Practices badge
CII best practices is self assessing badge for Open source project to be friendly and easy to contribute to as well as making sure the software is delivered in good quality.
As part of self-assessment, I identified several gaps that I am trying to address with this MR. I tried to write some rules for pull requests, issues and involvement in the project that I observed and pulled from spice guidelines to have them written in one place. If there is something not correct, please let me know. About security issues, I added a mail to @fziglio as he was recently active here, but if I should add someone else, let me know (@teuf ?). I can also assign different people for the project on CII you would be interested in contributing there.