Task: improve the "Using issue tracker" section

The Using issue tracker page seems to describe how to use issue tracker for people who want to report a bug and how to help triage issue.

Seeing this is the developer's guide (aka contributing to Python guide), it would be great if there are sections dedicated for how to search for issues to start contributing.
Even the section about what each fields in the issue tracker mean, perhaps it can be moved outside of the "triaging" section. Those info are useful for general contributors too, not just for triagers. A first time contributor might decide to skip that section entirely, because they don't have triage role, and therefore missing out important information.

从 devguide.python.org/tracker/ 的 Using issue tracker 页面以及 triaging 页面中的 Fields in the issue tracker 部分开始。查看贡献者目前如何查找 issue，并决定字段说明应放在哪里。当指南包含面向贡献者的 issue 搜索指导，并且无需进入 triaging 也能找到字段信息时，即视为完成。