Change project description on GitHub

[tsujp]

The current description is verbose and favours crediting protofire before describing what is actually does for sentence 2.

Solhint is an open source project created by https://protofire.io. Its goal is to provide a linting utility for Solidity code.

A better, concise description would be

Open source linter for Solidity.

It is already apparent that this is a project from protofire as there is protofire / solhint in the top-left on GitHub not to mention the repo's location is https://github.com/protofire/solhint.