Add Roundup Issue Tracker to the Ticketing section. (#2855)
The Roundup Issue Tracker is celebrating its 20th anniversary. It has been the tracking software for bugs.python.org since 2006. Please consider adding this software under active development to your list.
- [OTOBO](https://otobo.de/en/) - Flexible web-based ticketing system used for Customer Service, Help Desk, IT Service Management. ([Demo](https://otobo.de/en/open-source-ticketing-system/#demos), [Source Code](https://github.com/RotherOSS/otobo)) `GPL-3.0``Perl`
- [Pachno](https://pach.no/) - Bring your team together to design, build and deliver your project with a tool that works with you and your team, and adapts when you need to. ([Source Code](https://github.com/pachno/pachno)) `MPL-2.0``PHP`
- [Roundup Issue Tracker](https://www.roundup-tracker.org/) - A simple-to-use and -install issue-tracking system with command-line, web, REST, XML-RPC, and e-mail interfaces. Designed with flexibility in mind - not just another bug tracker. ([Source Code](https://www.roundup-tracker.org/code.html)) `MIT/ZPL-2.0``Python`
- [Sentry On-Premise](https://github.com/getsentry/onpremise) - A powerful error tracking platform with wide language support and a robust API. ([Source Code](https://github.com/getsentry/sentry)) `BSD-3-Clause``Python/Django`
- [Trudesk](https://trudesk.io/) - Trudesk is an open-source help desk/ticketing solution. ([Source Code](https://github.com/polonel/trudesk)) `Apache-2.0``Nodejs`