Update Exchange documention about retries
Update Exchange documention about retries

Exchange does not fallback to tcp, nor will retry the query. Make
this more clear.

tempbottle/dns,curtiszimmerman/dns,miekg/dns,benbearchen/dns,jdef/dns,rolandshoemaker/dns,jmhodges/dns,ym/go-dns,bboreham/dns,janstk/dns,Git-Host/dns,skyportsystems/dns,flebarbe/dns,ErikDubbelboer/dns,Psiphon-Inc/dns,cloudflare/dns,josephyzhou/dns,letsencrypt/dns,AlexCheong/dns,bragr/dns,skynet/dns,asergeyev/dns,tsenart/dns,hugozhu/dns,ezoic/dns,modulexcite/dns,FiloSottile/dns,michaelharo/dns