updated readme for custom setTitleBarDrawingBlock
updated readme for custom setTitleBarDrawingBlock

sdesimone/INAppStoreWindow,xvtom/INAppStoreWindow,sdesimone/INAppStoreWindow,cparnot/INAppStoreWindow,appden/INAppStoreWindow,xvtom/INAppStoreWindow,indragiek/INAppStoreWindow,indragiek/INAppStoreWindow,appden/INAppStoreWindow,cparnot/INAppStoreWindow