Sync SDL2 wiki -> header

[ci skip]

docs/README-platforms.md

@@ -4,5 +4,4 @@ Platforms
 We maintain the list of supported platforms on our wiki now, and how to
 build and install SDL for those platforms:
 
-    https://wiki.libsdl.org/Installation
-
+    https://wiki.libsdl.org/SDL2/Installation