Add configuration guide to rust-ide

[Livb-VRC]

I noticed that go-ide and a bunch of other language branches have a mini configuration guide with the mason packages you gotta install

It'd be great if rust-ide (and all branches in general) had something like this

[kjczarne]

I'm new to LunarVim and it took me a substantial amount of time that I need to do :MasonInstall codelldb for the config to work. I think adding this to the readme would be of great value for beginners.