Document the Debain Package

[niccokunzmann]

icalendar has a debian package:

sudo apt-get install python-icalendar

To close the issue:

• link to the package website e.g. https://tracker.debian.org/pkg/python-icalendar
• add the installation method for Debian/Ubuntu

File to change: install.html

See also:

• https://github.com/niccokunzmann/python-recurring-ical-events/pull/162/files

[niccokunzmann]

I got feedback from the maintainer of https://tracker.debian.org/pkg/python-icalendar: We can document this install method.