docs: more docs for nodemon as child process (#1362)

I was trying to find out how to use nodemon as child process, and stumble upon this https://github.com/remy/nodemon/issues/1018

So adding more docs for other people later to make it clearer how to do it.

[skip ci]

README.md

@@ -125,6 +125,10 @@ Note that if you specify a `--config` file or provide a local `nodemon.json` any
 
 Please see [doc/requireable.md](doc/requireable.md)
 
+## Using nodemon as child process
+
+Please see [doc/events.md](doc/events.md#Using_nodemon_as_child_process)
+
 ## Running non-node scripts
 
 nodemon can also be used to execute and monitor other programs. nodemon will read the file extension of the script being run and monitor that extension instead of .js if there's no `nodemon.json`:

doc/events.md

@@ -47,11 +47,29 @@ nodemon.emit('restart');
 nodemon.emit('quit');
 ```
 
+## Using nodemon as child process
+
 If nodemon is a spawned process, then the child (nodemon) will emit message
 events whereby the event argument contains the event type, and instead of
 emitting events, you `send` the command:
 
 ```js
+// using `spawn` as example, can use other functions like `fork`, etc
+// https://nodejs.org/api/child_process.html
+const { spawn } = require('child_process');
+
+function spawnNodemon() {
+  const cp = spawn('nodemon', ['path/to/file.js', '--watch', 'path/to/watch'], {
+    // the important part is the 4th option 'ipc'
+    // this way `process.send` will be available in the child process (nodemon)
+    // so it can communicate back with parent process (through `.on()`, `.send()`)
+    // https://nodejs.org/api/child_process.html#child_process_options_stdio
+    stdio: ['pipe', 'pipe', 'pipe', 'ipc'],
+  });
+
+  return cp;
+}
+
 var app = spawnNodemon();
 
 app.on('message', function (event) {