typo in n01_dynamics_overview.ipynb

[GitYiheng]

"Addition" part:
"mutally orthoganl vectors" -> "mutually orthogonal vectors"
"The magnitude of a vector can be found with::" -> "The magnitude of a vector can be found with:"

"Derivatives of vectors" part:
"Here, we have benefitted from the fact that..." -> "Here, we have benefited from the fact that"