add mailto feedback link with page as subject to wiki footer/header

[FlxVctr]

Example for existing footer link:

smo-wiki/docs/_layouts/default.html

Line 78 in 14f427c

<a href="https://github.com/Leibniz-HBI/Social-Media-Observatory/wiki/{{page.title}}/_edit">[edit the edge version of

[FlxVctr]

Code für Mailto Link hier einfügen:

https://github.com/Leibniz-HBI/smo-wiki/blob/main/docs/_layouts/default.html#L68

Jekyll Docs: https://jekyllrb.com/docs/