github: Creating issue: Add external links

github: Creating issue: Add external links

This is heavily inspired by OpenWrt main repository [1]
as in the packages feed we would like to follow
and be in sync with the main repository.

Having external, well, contact links, where users
can ask or propose feature request and even find links
for documentation or contacting us is a good idea.
Might help to improve the current state of this repository.

[1] https://github.com/openwrt/openwrt/blob/57c104ef7f8619d48579ada5ab24f78984391edd/.github/ISSUE_TEMPLATE/config.yml

Signed-off-by: Josef Schlehofer <redacted>