Running will not make you a faster cyclist, cycling will.
Some benefits to running include, most return on fitness in a short amount of time, little equipment needed, you can run anywhere at any time, and the the impact of running help build bone density.
Some problems with running include, higher risk of injury due to impact exercise, due to the ease of running a higher probability of over training, and it can be addictive.
In my experience the only form of exercise that can possibly make you a faster cyclist is swimming. The hypoxic nature of swimming can be beneficial to time trials. However you can achieve the same result through fast intervals on the bike. Ymmv.