README: update compile howto to include new buildroot configuration

README.md

@@ -11,14 +11,16 @@ Build
 
 Download:
 ```
-cd your_work_dir
 git clone git://git.buildroot.net/buildroot
+cd buildroot
+git checkout 2015.02
 ```
   
 Configure:
 ```
 cd buildroot
-make menuconfig
+cp ../buildroot.config .config
+make oldconfig
 ```
 In Target Options select Target Architecture as MIPS (big endian) and Target Architecture Variant as mips 32r2.
 In Toolchain select GCC Compiler version as gcc 4.7.x.
@@ -26,7 +28,7 @@ Save and exit.
 
 Build:
 ```
-make
+make toolchain
 ```
 
 2) Build Caraboot image