Add build instructions.

Author: Pavel Kovalenko

doc/howto/build.txt

@@ -0,0 +1,24 @@
+By default, all libraries mentioned below (except Windows/DirectX SDK) are assumed to be in the directory
+defined by XRAY_16X_LIBS environment variable.
+
+To build X-Ray Engine you'll need following libraries:
+  * OpenAutomate: https://developer.nvidia.com/openautomate
+  * NVAPI: https://developer.nvidia.com/nvapi
+  * libjpeg: http://sourceforge.net/projects/libjpeg
+    - Use "jpeg" as project root directory name for compatibility with CxImage
+  * zlib: http://zlib.net
+  * BugTrap: https://github.com/nitrocaster/BugTrap
+  * FreeImage: http://freeimage.sourceforge.net
+  * FreeMagic
+  * libogg-1.1.4: http://xiph.org/downloads
+  * libtheora-1.1.1: http://xiph.org/downloads
+  * libvorbis-1.2.3: http://xiph.org/downloads
+  * Autodesk Maya 2008/2009 SDK
+  * Autodesk 3DS Max 6.0 SDK
+  * Windows SDK: http://www.microsoft.com/en-us/download/details.aspx?id=8279
+  * DirectX SDK June 2010: http://www.microsoft.com/en-us/download/details.aspx?id=6812
+    - replace dxguid.lib with the one from Windows SDK
+      (for DirectPlay GUIDs)
+
+You can download all these libraries (except Windows/DirectX SDK) with compiled binaries here:
+https://dl.dropboxusercontent.com/u/63973281/dev/xray/xray-16-libraries.7z