Feat: Add cvlinkedin and cvgithub

[kilianmh]

Personal information convenience commands for linkedin and github.

This might be helpful since many use these platforms in their cv.
For Github the name is also added to the create the hyperlink.
For Linkedin the first parameter is used for the hyperlink and the second for text that is displayed.

Do you like the idea? If yes, then is the code or okay or you want any changes?
Once you are satisfied, I can update the readme and template accordingly.

[PandaScience]

Hey, thanks for the contribution and sorry for the late reply!

LGTM. Would be great if you could add it to the docs as well. There might be no vertical space left in the template's sidebar, so feel free to just throw out sth. else. Maybe the phone number or the overleaf or github entry under "social network".