Fluid 5439: Adding some Prefs Framework files

@cindyli or @jobara:
This pull request adds the following files:

AuxiliarySchemaForPreferencesFramework.md
Builder.md
Enactors.md
PreferencesEditor.md
PrimarySchemaForPreferencesFramework.md

and updates README.md 

Missing the code highlight on `fluid.prefs.enactors`