Add keywords to package.json

[codeandcats]

Interestingly I noticed there are no keywords defined in package.json. I'm not sure if I accidentally removed them as part of the major update or if they were never there (can't be bothered checking hehe) but either way I think we should add them.

The keywords defined in the github repo would probably be a good start. I'd also add "tsdv-joi" as a keyword.