Add instructions for neovim

EDITORS.md

@@ -8,6 +8,7 @@ new H2 header in this file containing the instructions. -->
 
 - [Emacs LSP Mode](https://emacs-lsp.github.io/lsp-mode/page/lsp-ruby-lsp/)
 - [Emacs Eglot](#Emacs-Eglot)
+- [Neovim LSP](#Neovim-LSP)
 
 ## Emacs Eglot
 
@@ -19,3 +20,60 @@ put that in your init file:
  ```
 
 When you run `eglot` command it will run `ruby-lsp` process for you.
+
+## Neovim LSP
+The [nvim-lspconfig](https://github.com/neovim/nvim-lspconfig/blob/master/lua/lspconfig/server_configurations/ruby_ls.lua)
+plugin has support for Ruby LSP.
+
+Ruby LSP only supports pull diagnostics, and neovim versions prior to v0.10.0-dev-695+g58f948614 only support [publishDiagnostics](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_publishDiagnostics).
+Additional setup is required to enable diagnostics from Ruby LSP to appear in neovim.
+
+```lua
+-- textDocument/diagnostic support until 0.10.0 is released
+_timers = {}
+local function setup_diagnostics(client, buffer)
+  if require("vim.lsp.diagnostic")._enable then
+    return
+  end
+
+  local diagnostic_handler = function()
+    local params = vim.lsp.util.make_text_document_params(buffer)
+    client.request("textDocument/diagnostic", { textDocument = params }, function(err, result)
+      if err then
+        local err_msg = string.format("diagnostics error - %s", vim.inspect(err))
+        vim.lsp.log.error(err_msg)
+      end
+      if not result then
+        return
+      end
+      vim.lsp.diagnostic.on_publish_diagnostics(
+        nil,
+        vim.tbl_extend("keep", params, { diagnostics = result.items }),
+        { client_id = client.id }
+      )
+    end)
+  end
+
+  diagnostic_handler() -- to request diagnostics on buffer when first attaching
+
+  vim.api.nvim_buf_attach(buffer, false, {
+    on_lines = function()
+      if _timers[buffer] then
+        vim.fn.timer_stop(_timers[buffer])
+      end
+      _timers[buffer] = vim.fn.timer_start(200, diagnostic_handler)
+    end,
+    on_detach = function()
+      if _timers[buffer] then
+        vim.fn.timer_stop(_timers[buffer])
+      end
+    end,
+  })
+end
+
+require("lspconfig").ruby_ls.setup({
+  on_attach = function(client, buffer)
+    setup_diagnostics(client, buffer)
+  end,
+})
+```