Add instructions/links for different clients to README

[nwolverson]

coc.nvim - see #53

[andys8]

It took me quite some time to figure out how to pass settings. Other language servers mostly use initializationOptions which didn't work.

Here is an example (Vim/CoC):

    "purescript": {
      "command": "purescript-language-server",
      "args": ["--stdio"],
      "filetypes": ["purescript"],
      "trace.server": "off",
      "rootPatterns": ["bower.json", "psc-package.json", "spago.dhall"],
      "settings": {
        "purescript": {
          "addSpagoSources": true,
          "outputDirectory": "ls-output"
        }
      }
    }

[andys8]

I updated the CoC wiki example: https://github.com/neoclide/coc.nvim/wiki/Language-servers#purescript

[nwolverson]

Closing this issue as not directly actionable, information or PRs providing config for other clients is welcome but should be a separate issue/PR.