Also

• https://wiki.sagemath.org/SageMathExternalPackages (first list of bullet points) can be integrated
• https://doc.sagemath.org/html/en/faq/faq-contribute.html#i-am-not-a-programmer-is-there-another-way-i-can-help-out can be integrated into developer manual too

CC: @kwankyu

Component: documentation

Issue created by migration from https://trac.sagemath.org/ticket/34554