Resistance for relay coil
The direct answer is that you do not need a resistance in series when powering a 5 volt relay coil from 5 volt power supply.
   --  For more in depth understanding, go to the data sheet that you linked, and look at the coil data. -- From the coil data, you can calculate the amount of current required for the coil. 
   ---- Lots of in depth analysis can be made depending upon how you drive the relay coil.