lsp: remove references to LspInstall (#13738)

and adjust sumneko setup instructions

runtime/doc/lsp.txt

@@ -27,9 +27,9 @@ Follow these steps to get LSP features:
   1. Install the nvim-lspconfig plugin.  It provides common configuration for
      various servers so you can get started quickly.
      https://github.com/neovim/nvim-lspconfig
-  2. Install a language server.  Try ":LspInstall <tab>" or use your system
-     package manager to install the relevant language server:
+  2. Install a language server. A list of language servers can be found here:
      https://microsoft.github.io/language-server-protocol/implementors/servers/
+     See individual server documentation for installation instructions.
   3. Add `lua require('lspconfig').xx.setup{…}` to your init.vim, where "xx" is
      the name of the relevant config. See the nvim-lspconfig README for details.
      NOTE: Make sure to restart nvim after installing and configuring.
@@ -62,20 +62,39 @@ Example config (in init.vim): >
       vim.api.nvim_buf_set_option(0, 'omnifunc', 'v:lua.vim.lsp.omnifunc')
 
       -- For plugins with an `on_attach` callback, call them here. For example:
-      -- require('completion').on_attach(client)
+      -- require('completion').on_attach()
     end
 
     -- An example of configuring for `sumneko_lua`,
     --  a language server for Lua.
-    -- First, you must run `:LspInstall sumneko_lua` for this to work.
+
+    -- set the path to the sumneko installation
+    local system_name = "Linux" -- (Linux, macOS, or Windows)
+    local sumneko_root_path = '/path/to/lua-language-server'
+    local sumneko_binary = sumneko_root_path.."/bin/"..system_name.."/lua-language-server"
+
     require('lspconfig').sumneko_lua.setup({
+      cmd = {sumneko_binary, "-E", sumneko_root_path .. "/main.lua"};
       -- An example of settings for an LSP server.
       --    For more options, see nvim-lspconfig
       settings = {
         Lua = {
+          runtime = {
+            -- Tell the language server which version of Lua you're using (most likely LuaJIT in the case of Neovim)
+            version = 'LuaJIT',
+            -- Setup your lua path
+            path = vim.split(package.path, ';'),
+          },
           diagnostics = {
-            enable = true,
-            globals = { "vim" },
+            -- Get the language server to recognize the `vim` global
+            globals = {'vim'},
+          },
+          workspace = {
+            -- Make the server aware of Neovim runtime files
+            library = {
+              [vim.fn.expand('$VIMRUNTIME/lua')] = true,
+              [vim.fn.expand('$VIMRUNTIME/lua/vim/lsp')] = true,
+            },
           },
         }
       },