Broken links in CONTRIBUTING.md

[this-is-varunxyz]

Just noticed that a few links in CONTRIBUTING.md (like HSF Training, our License, and Code of Conduct) aren’t working — they lead to 404 pages.

[welcome]

Thanks for opening your first issue here 💖! If you have any questions, feel free to mention one of the conveners, previous contributors, or attend our weekly meeting (see https://hepsoftwarefoundation.org/workinggroups/training.html). Also, sometimes issues go unnoticed, so don't hesitate to @mention some of us, if we do not come back to you within a few days.

[eduardo-rodrigues]

Well spotted. Sure, assigning you. Thanks!

[stale]

This issue or pull request has been automatically marked as stale because it has not had recent activity. Please manually close it, if it is no longer relevant, or ask for help or support to help getting it unstuck. Let me bring this to the attention of @amorenobr @vlukashenko @richa2710 @michmx for now.