IrrlichtMt: Document Driver/Device compatibility

irr/README.md

@@ -36,6 +36,27 @@ We aim to support these platforms:
 
 This doesn't mean other platforms don't work or won't be supported, if you find something that doesn't work contributions are welcome.
 
+Compatibility matrix
+--------------------
+
+Driver (rows) vs Device (columns)
+
+|                           | SDL [1]  | Linux [2]      | OSX [3]          | Win32 [4]       |
+|---------------------------|----------|----------------|------------------|-----------------|
+| OpenGL 1.2 (to 2.1)       | Works    | Works (GLX)    | Works (NSOpenGL) | Works (WGL)     |
+| OpenGL 3.2+               | Works    | Testing (GLX)  | Not implemented  | Testing (WGL)   |
+| OpenGL ES 2.x             | Works    | Untested (EGL) | Not implemented  | Untested (EGL)  |
+| WebGL 1                   | Untested | Untested (EGL) | Not implemented  | Not implemented |
+| Null (no graphics output) | Works    | Works          | Works            | Works           |
+
+Notes:
+
+* [1] `CIrrDeviceSDL`: supports Android, Linux, macOS, Windows
+* [2] `CIrrDeviceLinux`: supports Linux
+* [3] `CIrrDeviceOSX`: supports macOS
+* [4] `CIrrDeviceWin32`: supports Windows
+
+
 License
 -------