Adding warnings and
As of this ticket (for Sage 9.8, assuming it can be released in January 2023), we keep the Trac instructions.
In a follow-up ticket (for Sage 9.9), we will remove the trac instructions, update the developer manual according to the transition guide, and add links to github command-line interface, e.g., https://cli.github.com/manual/gh_repo_fork
Part of Meta-ticket #30363: Migration from Trac to GitHub
CC: @kwankyu @soehms @tobiasdiez
Component: documentation
Author: Matthias Koeppe, Kwankyu Lee
Branch/Commit: cecbcac
Reviewer: Kwankyu Lee, Matthias Koeppe
Issue created by migration from https://trac.sagemath.org/ticket/34648