Updated README-platforms.md

Also added platform specific README files

docs/README-platforms.md

@@ -1,8 +1,40 @@
-Platforms
-=========
+# Platforms
 
-We maintain the list of supported platforms on our wiki now, and how to
-build and install SDL for those platforms:
+## Supported Platforms
 
-    https://wiki.libsdl.org/Installation
+- [Android](README-android.md)
+- [Emscripten](README-emscripten.md)
+- [FreeBSD](README-bsd.md)
+- [Haiku OS](README-haiku.md)
+- [iOS](README-ios.md)
+- [Linux](README-linux.md)
+- [macOS](README-macos.md)
+- [NetBSD](README-bsd.md)
+- [Nintendo Switch](README-switch.md)
+- [Nintendo 3DS](README-3ds.md)
+- [OpenBSD](README-bsd.md)
+- [PlayStation 2](README-ps2.md)
+- [PlayStation 4](README-ps4.md)
+- [PlayStation 5](README-ps5.md)
+- [PlayStation Portable](README-psp.md)
+- [PlayStation Vita](README-vita.md)
+- [RISC OS](README-riscos.md)
+- [SteamOS](README-steamos.md)
+- [tvOS](README-ios.md)
+- [Windows](README-windows.md)
+- [Windows GDK](README-gdk.md)
+- [Xbox](README-gdk.md)
 
+## Unsupported Platforms
+
+If your favorite system is listed below, we aren't working on it. However, if you send reasonable patches and are willing to support the port in the long term, we are happy to take a look!
+
+All of these still work with [SDL2](/SDL2), which is an incompatible API, but an option if you need to support these platforms still.
+
+- Google Stadia
+- NaCL
+- Nokia N-Gage
+- OS/2
+- QNX
+- WinPhone
+- WinRT/UWP