Update catkin_migration.rst
Update catkin_migration.rst

Fixed typos and added a comment about the <buildtool_depend> on catkin.
jack-oquin/catkin,beni55/catkin,asmodehn/catkin,shyamalschandra/catkin,meyerj/catkin,harmishhk/catkin,meyerj/catkin,thaddeustaylor/catkin,thaddeustaylor/catkin,scpeters/catkin,beni55/catkin,asmodehn/catkin,wkentaro/catkin,ros/catkin,shyamalschandra/catkin,meyerj/catkin,harmishhk/catkin,ros/catkin,beni55/catkin,scpeters/catkin,wkentaro/catkin,harmishhk/catkin,thaddeustaylor/catkin,jack-oquin/catkin,scpeters/catkin,jack-oquin/catkin,ros/catkin,wkentaro/catkin,asmodehn/catkin,shyamalschandra/catkin