doc: improve process.platform

PR-URL: #18057
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

doc/api/process.md

@@ -1439,13 +1439,26 @@ added: v0.1.16
 * {string}
 
 The `process.platform` property returns a string identifying the operating
-system platform on which the Node.js process is running. For instance
-`'darwin'`, `'freebsd'`, `'linux'`, `'sunos'` or `'win32'`
+system platform on which the Node.js process is running.
+
+Currently possible values are:
+
+* `'aix'`
+* `'darwin'`
+* `'freebsd'`
+* `'linux'`
+* `'openbsd'`
+* `'sunos'`
+* `'win32'`
 
 ```js
 console.log(`This platform is ${process.platform}`);
 ```
 
+The value `'android'` may also be returned if the Node.js is built on the
+Android operating system. However, Android support in Node.js
+[is experimental][Supported platforms].
+
 ## process.ppid
 <!-- YAML
 added: v9.2.0
@@ -2017,5 +2030,6 @@ cases:
 [Readable]: stream.html#stream_readable_streams
 [Signal Events]: #process_signal_events
 [Stream compatibility]: stream.html#stream_compatibility_with_older_node_js_versions
+[Supported platforms]: https://github.com/nodejs/node/blob/master/BUILDING.md#supported-platforms-1
 [TTY]: tty.html#tty_tty
 [Writable]: stream.html#stream_writable_streams