Add a script to automatically add rules to the README

[Alex Saunders]

There is currently an executable script (courtesy of eslint-plugin-jsx-a11y) to set up the boilerplate for a new linting rule (adding the rule src file, tests etc.) - using the same information given to this script we can add the new rule and it's description to the README automatically.

Obviously not a critical issue as adding new rules to the README is easy enough - automating it would just avoid any forgetfulness.