Add tags to repo

[anki-code]

Hi! Thank you for the useful xontrib!

Please add xonsh and xontrib tags to the repo:

It helps spread the word about xontrib on Github.

Thanks!

[scopatz]

Thanks!

[anki-code]

Great! Thanks!

I asked some xontributors to add social preview images to the xontribs and if you review the Github xontrib topic and scroll down you'll see the nice screenshots! This could be used in building xontribs page in xonsh docs.