Add a warning and example about ordering collection with custom dates. (#871)
Add a warning and example about ordering collection with custom dates. (#871)

Co-authored-by: Fabien Basmaison <777bcfcf9efee56bedca63c5eb2304e67df52892@arkhi.org>
getgrav/grav-learn,getgrav/grav-learn,getgrav/grav-learn,getgrav/grav-learn