Deprecate and update readme to recommend a solution that uses a language server

[TSMMark]

I used this misogi/vscode-ruby-rubocop vs code extension for many many years, but it's time to deprecate this package and recommend a solution that uses a language server like https://github.com/Shopify/ruby-lsp

The performance difference is unbelievable. Booting rubocop executable every time your IDE needs to lint is just not the proper way to do it. This plugin is much slower, and costs a lot of extra work for your dev machine.