add instructions for clang, use markdown format

README.md

@@ -0,0 +1,50 @@
+Requirements
+============
+
+- C++11 compatible compiler
+- GMP (GNU multiprecision library)
+  http://gmplib.org/
+- (optional) gperftools
+  https://code.google.com/p/gperftools/
+- cmake
+  http://www.cmake.org
+
+Instructions for DEBUG build
+
+    mkdir -p build/debug
+    cd build/debug
+    cmake -DCMAKE_BUILD_TYPE=DEBUG ../../src
+    make
+
+Instructions for RELEASE build
+
+    mkdir -p build/release
+    cd build/release
+    cmake -DCMAKE_BUILD_TYPE=RELEASE ../../src
+    make
+
+Instructions for installing gcc-4.8 (C++11 compatible) on Ubuntu
+
+    sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y
+    sudo update-alternatives --remove-all gcc
+    sudo update-alternatives --remove-all g++
+    sudo apt-get update
+    sudo apt-get install g++-4.8 -y
+    sudo apt-get upgrade -y && sudo apt-get dist-upgrade -y
+
+Instructions for installing clang-3.3 (C++11 compatible) on Ubuntu
+
+    sudo add-apt-repository ppa:h-rayflood/llvm
+    sudo apt-get update
+    sudo apt-get dist-upgrade
+    sudo apt-get install clang-3.3 clang-3.3-doc
+
+Note that you [still need][1] to have g++-4.8's C++ runtime library to
+support some C++11 features that we are using.
+
+You can specify the C++ compiler to use by using ``-DCMAKE_CXX_COMPILER``
+option. For example
+
+    cmake -DCMAKE_BUILD_TYPE=DEBUG -DCMAKE_CXX_COMPILER=clang++-3.3 ../../src
+
+[1]: http://clang.llvm.org/cxx_status.html