fix geometry tutorial regarding the need to specify the "mode"
fix geometry tutorial regarding the need to specify the "mode"

mjbshaw/Eigen,mjbshaw/Eigen,madlib/eigen_backup,mjbshaw/Eigen,rotorliu/eigen,rotorliu/eigen,rotorliu/eigen,rotorliu/eigen,madlib/eigen_backup,mjbshaw/Eigen,madlib/eigen_backup,madlib/eigen_backup