Added note to pcl_visualizer tutorial
Added note to pcl_visualizer tutorial

Addresses #1465. Warns about the current limitations of keyboard and mouse interaction in VTK for Mac platforms.

ipa-rmb/pcl,kanster/pcl,damienjadeduff/pcl,drmateo/pcl,damienjadeduff/pcl,kanster/pcl,mikhail-matrosov/pcl,mikhail-matrosov/pcl,drmateo/pcl,stefanbuettner/pcl,lebronzhang/pcl,drmateo/pcl,damienjadeduff/pcl,ipa-rmb/pcl,kanster/pcl,stefanbuettner/pcl,ipa-rmb/pcl,lebronzhang/pcl,mikhail-matrosov/pcl,wgapl/pcl,damienjadeduff/pcl,kanster/pcl,wgapl/pcl,lebronzhang/pcl,KevenRing/pcl,KevenRing/pcl,stefanbuettner/pcl,lebronzhang/pcl,mikhail-matrosov/pcl,stefanbuettner/pcl,KevenRing/pcl,drmateo/pcl,stefanbuettner/pcl,KevenRing/pcl,wgapl/pcl,KevenRing/pcl,wgapl/pcl,drmateo/pcl,kanster/pcl,ipa-rmb/pcl,damienjadeduff/pcl,wgapl/pcl,lebronzhang/pcl,ipa-rmb/pcl,mikhail-matrosov/pcl