add some basic build instructions and license info

readme.txt

@@ -1,6 +1,50 @@
 
 Bullet 3.x GPU rigid body pipeline.
 
-See docs folder for information, 
+License
-including how to build the project.
+All source code files are licensed under the permissive zlib license
+(http://opensource.org/licenses/Zlib) unless marked differently in a particular folder/file.
+
+
+Build instructions:
+
+Windows:
+Click on build3/vs2010.bat and open build3/vs2010/0MySolution.sln
+
+Linux and Mac OSX gnu make
+In a terminal type:
+
+cd build3
+
+Dependend on your system (Linux 32bit, 64bit or Mac OSX) use one of the following lines
+./premake_linux gmake
+./premake_linux64 gmake
+./premake_osx gmake
+
+Then
+
+cd gmake
+make
+
+Mac OSX Xcode
+Click on build3/xcode4.command or in a terminal window execute
+./premake_osx xcode4
+
+Usage:
+
+The main demo executable will be located in the bin folder.
+The demo starts with App_Bullet3_OpenCL_Demos_*
+
+You can just run it though a terminal/command prompt, or by clicking it.
+
+
+There are some command-line options, you can see using the --help option. For example, this will perform a benchmark writing to some files:
+
+./App_Bullet3_OpenCL_Demos_clew_gmake --benchmark
+
+You can use the mouse to grab objects. When holding the ALT of CONTROL key, you have Maya style camera mouse controls.
+Press F1 to create a screenshot.
+Hit ESCAPE to exit the demo app.
+
+See docs folder for further information.