docs: add heimanba as a contributor for code

[allcontributors[bot]]

Add @heimanba as a contributor for code.

This was requested by webup in this comment

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}