Add example of apply_ufunc (#421)

* add apply_ufunc example

* rename

* some beautifications

* including review remarks

* not example, it's a recipe

* few tweaks

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Co-authored-by: jemmajeffree <jj8842@gadi-cpu-bdw-0003.gadi.nci.org.au>
Co-authored-by: Navid C. Constantinou <navidcy@users.noreply.github.com>

Author: 3 people