Brown spots on rhododendron
Your rhododendron was damaged during one or more of the recent bright sunny days. The dry brown areas are dead whereas the off-color areas have sub-lethal damage.
More than likely, the shrub was short of water at the time of the damage because the roots haven't yet extended into the soil surrounding the planting hole. To help the shrub survive the summer in fine condition, be certain to apply water directly to the original rootball.
The general guide to establish a woody plant is to water it as needed for at least the first 2 years. Then, for your rhododendron, plan to water it at least once a month during our summers.