add dns element documentation to readme
add dns element documentation to readme

mzdravkov/circuit,beni55/circuit,cgvarela/circuit,mjolk/circuit,beni55/circuit,rranshous/circuit,cgvarela/circuit,mzdravkov/circuit,bzz/circuit,rranshous/circuit,cgvarela/circuit,mjolk/circuit,lgscofield/circuit,mzdravkov/circuit,ebookbug/circuit,rranshous/circuit,beni55/circuit,tonestuff/circuit,bzz/circuit,rranshous/circuit,tonestuff/circuit,mjolk/circuit,cgvarela/circuit,tonestuff/circuit,lgscofield/circuit,mjolk/circuit,lgscofield/circuit,mzdravkov/circuit,lgscofield/circuit,ebookbug/circuit,bzz/circuit,tonestuff/circuit,beni55/circuit,ebookbug/circuit,ebookbug/circuit,bzz/circuit