doc-byte-sized-tasks: Add link to the byte-sized tasks in CONTRIBUTING

Thanks to @adampalay, we now have a list of byte-sized tasks, which are useful for new contributors who want a gentle introduction to the platform. This PR adds a link to the tasks tagged as byte-sized in the public tracker.
I feel like it might be worth mentioning that people should first make a JIRA account, and then comment on the bugs to indicate they are working on them, to ask clarifying questions, etc.