I didn't find anything in QlikSense that would allow me to do this, but if you're using Qlikview you can always try to create a text object with transparent background and layer set as "Top" in properties. Screenshot you attached suggest you're using QlikView, so you should definately be able to achieve this by using this simple work around.
AFAIK, qliksense default pie chart doesn't not have this feature, (where as qlikview bar chart has time feature.. may be they will include in feature qliksense version). for you you can try to search if there any extension available in qlik branch. tks