translation: update insertion_sort.md

[SamJin98]

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[K3v123]

Hi Sam
thanks for the hard work. here are some of my suggestions.

kind regards

[K3v123]

I had a second thought about the 'key' part. if its in the insertion sort section, then it should be fine.... other than that its just what Krahets suggested... if its a new PR I will approve that one again.

thanks for the hard work!

sincerely,
Kevin