[Backlog for iOS] Issue templates, @mentions in pull request comments

Backlog for iOS has the following updates:

Issue templates: You can create and edit issue templates right in the app. Issue templates are great for informing users how to fill in the fields/required information for the issue. Learn more about them in this post: Issue Templates

@mentions in pull request comments: Notify members in your pull request comments by using @mentions. See how mentions work in our post: @mentions for notifying members and teams