[DOC] Update developer notes

Summary:
This makes the instructions use cmake/ninja and adds some details when
necessary, especially for running the sanitizers as requested in D5391.

Depends on D5321.

Test Plan: Read the doc and try the instructions.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: jasonbcox, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D5395