add citation for the lesson

[ajrominger]

this is a nice example to base ours on: https://github.com/alan-turing-institute/the-turing-way/blob/main/CITATION.cff

[diazrenata]

added 638332b.

Need to discuss author order (current is andy first + random number generator), license (Carpentries uses CC).

No DOI/archive yet :)

[diazrenata]

Also, @Rilquer, @jidec, @isaacovercast could you send me your ORCIDs or just populate them in the CITATION.cff file in this branch?