pkg/fall: add (a lot of) guidance (#3450)
pkg/fall: add (a lot of) guidance (#3450)

update the pkg doc to talk about various trade off

Fixes #2723

Signed-off-by: Miek Gieben <00b357f94cf3a1145a32703fb42e2d80418ab806@miek.nl>
miekg/coredns,coredns/coredns,chrisohaver/coredns,yongtang/coredns,johnbelamaric/coredns,miekg/coredns,johnbelamaric/coredns