README: Updates build commands.

README.md

@@ -326,8 +326,9 @@ git clone --recursive https://github.com/sass/node-sass.git
 cd node-sass
 git submodule update --init --recursive
 npm install
-npm install -g node-gyp
-node-gyp rebuild  # to make debug release, use -d switch
+node scripts/build -f  # use -d switch for debug release
+# if succeeded, it will generate and move
+# the binary in vendor directory.
 ```
 
 ## Command Line Interface