doc: file-change-detect [ci skip]

runtime/doc/if_lua.txt

@@ -416,20 +416,46 @@ Example: repeating timer
     print('sleeping');
 
 
+Example: File-change detection				*file-change-detect*
+    1. Save this code to a file.
+    2. Execute it with ":luafile %".
+    3. Use ":Watch %" to watch any file.
+    4. Try editing the file from another text editor.
+    5. Observe that the file reloads in Nvim (because on_change() calls
+       |:checktime|). >
+
+    local w = vim.loop.new_fs_event()
+    local function on_change(err, fname, status)
+      -- Do work...
+      vim.api.nvim_command('checktime')
+      -- Debounce: stop/start.
+      w:stop()
+      watch_file(fname)
+    end
+    function watch_file(fname)
+      local fullpath = vim.api.nvim_call_function(
+        'fnamemodify', {fname, ':p'})
+      w:start(fullpath, {}, vim.schedule_wrap(function(...)
+        on_change(...) end))
+    end
+    vim.api.nvim_command(
+      "command! -nargs=1 Watch call luaeval('watch_file(_A)', expand('<args>'))")
+
+
 Example: TCP echo-server				*tcp-server*
     1. Save this code to a file.
     2. Execute it with ":luafile %".
     3. Note the port number.
     4. Connect from any TCP client (e.g. "nc 0.0.0.0 36795"): >
 
-    local function create_server(host, port, on_connection)
+    local function create_server(host, port, on_connect)
       local server = vim.loop.new_tcp()
       server:bind(host, port)
       server:listen(128, function(err)
         assert(not err, err)  -- Check for errors.
         local sock = vim.loop.new_tcp()
         server:accept(sock)  -- Accept client connection.
-        on_connection(sock)  -- Start reading messages.
+        on_connect(sock)  -- Start reading messages.
       end)
       return server
     end