Add pkgcheck action

[damianooldoni]

Based on inbo/camtrapdp#84:

See https://github.com/ropensci-review-tools/pkgcheck-action, recommended by rOpenSci

Nice to have.

[PietrH]

Leaving this here as a note for future me:

pkgcheck::use_github_action_pkgcheck()

[wolfmissotten]

PR #382 fixes this issue.