Document setup instructions for some editors

[smorimoto]

For example, using OCaml-LSP with Sublime is going to be easier with this PR sublimelsp/LSP#2386, but I think there are some pitfalls, such as having to launch the editor with opam exec -- subl . if you want to use it with the local switch. Documenting such pitfalls may help newcomers.

[jfeser]

If you want to write up some documentation, I think would be a reasonable thing to add to the wiki.