Add missing repositories to source code page

[CONIGUERO]

Looking at the production architecture diagram on the README, I noticed two repos missing from the source code page on the website.

sandbag-bot: https://github.com/kraktus/zulip-sandbag-bot
cr-bot: https://github.com/benediktwerner/CR-bot

Would be nice if those were added. I would have made a PR but from a cursory glance it appears the page's contents are tracked through an internal CMS API and not the git repo.