doc: add unhandledRejection to strict mode

`lib/internal/process/promises.js` contains the following comment
about --unhandled-rejections=strict. This commit updates the
docs to reflect this:

// --unhandled-rejections=strict:
// Emit 'uncaughtException'. If it's not handled, print
// the error to stderr and exit the process.
// Otherwise, emit 'unhandledRejection'. If
// 'unhandledRejection' is not
// handled, emit 'UnhandledPromiseRejectionWarning'.

Fixes: nodejs#41184

Author: cjihrig

doc/api/cli.md

@@ -1254,7 +1254,8 @@ occurs. One of the following modes can be chosen:
 
 * `throw`: Emit [`unhandledRejection`][]. If this hook is not set, raise the
   unhandled rejection as an uncaught exception. This is the default.
-* `strict`: Raise the unhandled rejection as an uncaught exception.
+* `strict`: Raise the unhandled rejection as an uncaught exception. If the
+  exception is handled, [`unhandledRejection`][] is emitted.
 * `warn`: Always trigger a warning, no matter if the [`unhandledRejection`][]
   hook is set or not but do not print the deprecation warning.
 * `warn-with-error-code`: Emit [`unhandledRejection`][]. If this hook is not