Update links in CONTRIBUTE.md
Update links in CONTRIBUTE.md

Summary:
Update Michael Lynch's to his latest iterration, which is better put together.

Update John Carmak's link because gamasutra has been unreliable.

Test Plan: Read

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9263

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