Add a solhint config and a GUIDELINES

[0xtekgrinder]

Is your feature request related to a problem? Please describe.
When I started to check out the code of this repository and wanted to contribute, one of my first questions was how should I code an d I haven't fond anything to help me.

Describe the solution you'd like
Add a solhint configuration as well as a guidelines defining the way to code for exemple: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/GUIDELINES.md

Additional context
On most of the opensource repositories with solidity smart contracts there is a solhint config and guidelines