Update reference to contributing file

[emmanuel-ferdman]

Small PR - PR #1166 moved the location of the CONTRIBUTING.md. This PR adjusts sources to changes.

[CLAassistant]

All committers have signed the CLA.

[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.}

[hslatman]

Thank you, @emmanuel-ferdman 🙂