docs: clarify how to handle SIGUSR2

Fixes #1889

README.md

@@ -292,9 +292,10 @@ nodemon sends a kill signal to your application when it sees a file update. If y
 The following example will listen once for the `SIGUSR2` signal (used by nodemon to restart), run the clean up process and then kill itself for nodemon to continue control:
 
 ```js
-process.once('SIGUSR2', function () {
+// important to use `on` and not `once` as nodemon can re-send the kill signal
+process.on('SIGUSR2', function () {
   gracefulShutdown(function () {
-    process.kill(process.pid, 'SIGUSR2');
+    process.kill(process.pid, 'SIGTERM');
   });
 });
 ```

faq.md

@@ -353,8 +353,10 @@ Your application will likely be running the old version code if you see that mes
 A common cause for this is when graceful shutdowns are doing async tasks, i.e:
 
 ```
-process.once('SIGUSR2', async () => {
+// ensure this is `on` and not `once`
+process.on('SIGUSR2', async () => {
   await db.disconnect()
+  process.kill(process.pid, 'SIGTERM');
 })
 ```