Remove reference to GNURADIO_ROOT

git-svn-id: https://svn.code.sf.net/p/gnss-sdr/code/trunk@285 64b25241-fba3-4117-9849-534c7e92360d

README

@@ -3,8 +3,8 @@ HOW TO BUILD GNSS-SDR
 
 This document describes how to set up the compilation environment and build GNSS-SDR. See also http://gnss-sdr.org/documentation/building-guide
 
-Ubuntu 11.04, 11.10, 12.04 (32 and 64 bits)
---------------------------------------------
+Ubuntu 11.04, 11.10, 12.04, 12.10 (32 and 64 bits)
+--------------------------------------------------
 
 * Install GNU Radio:
 
@@ -19,7 +19,6 @@ This can take a while (up to two hours to complete, depending on your system), a
 - Set up some system variables needed by the GNSS-SDR build system:
 
 export PYTHONPATH=/usr/local/lib/python2.7/dist-packages
-export GNURADIO_ROOT=/path/to/gnuradio
 export LD_LIBRARY_PATH=/usr/local/lib
 
 where /path/to/gnuradio is the folder in which you invoked build-gnuradio. In order to avoid defining these variables each time you enter a session, you may want to add these three lines to your $HOME/.bashrc file.
@@ -169,8 +168,13 @@ $ bjam release
 
 Mac OS X 
 ------------------------------
-NOTE: Currently, Apple's GCC toolchain is broken. We are working towards the use of LLVM/Clang.
+NOTE: Currently, Apple's GCC toolchain is broken. We are working towards the use of LLVM/Clang. 
 
+WARNING: GNU Radio's VOLK component (which handles vector optimized instructions and routines) compiles best when using GCC. 
+The default compiler for macports is CLANG, which will result in a fully functioning GNU Radio install but the VOLK component will not utilize the CPU's capabilities.
+In order to take advantage of VOLK, compile it with the (rather old) GCC 4.2:
+
+$ sudo port install gnuradio-devel +grc +python27 +uhd +orc +swig +qtgui +wxgui configure.compiler=llvm-gcc-4.2
 
 
 GETTING STARTED