SDL example: hasty readme.

examples/sdl_opengl_example/README.md

@@ -0,0 +1,10 @@
+
+# How to Build
+
+- On Windows with Visual Studio's CLI
+
+\<sdl2path\> is your SDL2 folder.
+
+```
+cl /MD /I <sdl2path\include> /I ..\.. main.cpp imgui_impl_sdl.cpp ..\..\imgui.cpp /link /LIBPATH:<sdl2path\lib> SDL2.lib SDL2main.lib
+```