Documentation "Introduction" - added paragraph about macros define before including headers. Issue #36 Thanks @chaoticbob !

Author: adam-sawicki-a

src/vk_mem_alloc.h

@@ -123,6 +123,13 @@ To do it properly:
 
 It may be a good idea to create dedicated CPP file just for this purpose.
 
+Please note that this library includes header `<vulkan/vulkan.h>`, which in turn
+includes `<windows.h>` on Windows. If you need some specific macros defined
+before including these headers (like `NOMINMAX`, `WIN32_LEAN_AND_MEAN`, or
+`WINVER` for Windows, `VK_USE_PLATFORM_WIN32_KHR` for Vulkan), you must define
+them before every `#include` of this library.
+
+
 \section quick_start_initialization Initialization
 
 At program startup: