Updated documentation to include instructions to install protobuf with Python support on Mac OS X

docs/installation.md

@@ -135,7 +135,8 @@ In other `ENV` settings, things may not work as expected.
 Simply run the following:
 
     brew install --build-from-source --with-python boost
-    for x in snappy leveldb protobuf gflags glog szip lmdb homebrew/science/opencv; do brew install $x; done
+    brew install --with-python protobuf
+    for x in snappy leveldb gflags glog szip lmdb homebrew/science/opencv; do brew install $x; done
 
 Building boost from source is needed to link against your local Python (exceptions might be raised during some OS X installs, but **ignore** these and continue). If you do not need the Python wrapper, simply doing `brew install boost` is fine.