doc(README.md): Boost support

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>

README.md

@@ -27,7 +27,9 @@ Requirements
 - [MPFR (GNU MPFR Library)](http://www.mpfr.org/)
 - [Lua 5.2 or 5.1](http://www.lua.org), or [LuaJIT 2.0](http://luajit.org)
 - (optional) [gperftools](https://code.google.com/p/gperftools/)
-
+- (optional) [Boost](http://www.boost.org) (version >= 1.54), we can
+  build Lean using boost::thread instead of std::thread. When using
+  Boost, Lean can modify the thread stack size.
 
 Installing required packages at
 --------------------------------

doc/make/ubuntu-12.04-detailed.md

@@ -26,6 +26,10 @@ Preparing working environment on Ubuntu 12.04
     sudo apt-get install doxygen
     sudo apt-get install kcachegrind
 
+    sudo add-apt-repository --yes ppa:boost-latest/ppa
+    sudo apt-get install libboost1.54-dev
+    sudo apt-get install libboost-thread1.54-dev
+
 ### Fork Lean on github : https://github.com/leodemoura/lean
 
 ### Create a projects directory
@@ -46,6 +50,14 @@ Preparing working environment on Ubuntu 12.04
     cmake -D CMAKE_BUILD_TYPE=Debug ../../src
     make
 
+### Build Lean using Boost
+
+    cd lean
+    mkdir -p build/release
+    cd build/release
+    cmake -D CMAKE_BUILD_TYPE=Release -D BOOST=ON ../../src
+    make
+
 ### If you are using Emacs, here are some basic configurations
 
     (custom-set-variables