govc: Add object.collect type flag alias help
govc: Add object.collect type flag alias help

Add help text for type flag aliases for `object.collect`
subcommand to mirror help text provided for the `find`
subcommand (as suggested by @dougm).

refs vmware/govmomi#2491

bruceadowns/govmomi,vmware/govmomi,bruceadowns/govmomi,vmware/govmomi,bruceadowns/govmomi,vmware/govmomi