Document how to use ics-query with jcal

[niccokunzmann]

The ical2jcal package should be used in the documentation in a section for jCal.

To close:

• show ical2jcal and jcal2ical usage
• mention the RFC
• link to ical2jcal in command line help
• link to ical2jcal pypi package

[nguyenthekr92-byte]

I'd like to work on this bounty! I can handle documentation. I'll start working on this right away and submit a PR once done.