add pkgconfig to homebrew install instruction

Min RK · Min RK · commit ac26781e0f56 · 2013-04-23T12:06:43.000-07:00
build will not find freetype headers without it.

Alternate fix would be to search for freetype in the homebrew location (`/usr/local/Cellar/freetype/VERSION/`), or add the right location to the include path (`/usr/local/include/freetype2`).
diff --git a/README.osx b/README.osx
@@ -9,7 +9,7 @@ homebrew.
 
 Example usage::
 
-  brew install libpng freetype
+  brew install libpng freetype pkgconfig
 
 If you are using MacPorts, execute the following instead:
 
