Can I add links in backlog items, tasks, etc.?
Yes, there are optional link fields in backlog items, tasks, sprints, releases, and projects. You can use them to link to external information, such as a bug in a bug tracking system, or a page in a wiki.
To select which link fields to show in a project, open the project dialog (in the Projects page) and click "Settings" in the upper right corner of the dialog. Then find the link field settings and select which link fields to show.