improve hd keys docs
improve hd keys docs

bilthon/bitcore,bitpay/bitcore,olalonde/bitcore,maraoz/coinforge,martindale/bitcore,iobond/bitcore,MonetaryUnit/bitcore,lekkas/bitcore,bitpay/bitcore,iobond/bitcore,TeamPiggyCoin/PiggyCore,adjoinant/bitcore,pnagurny/bitcore,iobond/bitcore,bitjson/bitcore,bitjson/bitcore,bilthon/bitcore,TOMOAKI12345/bitcore,litecoin-project/litecore,TOMOAKI12345/bitcore,bitjson/bitcore,lekkas/bitcore,eordano/bitcore,bankonme/bitcore,daxxog/clamcore,genecyber/bitcore,TeamPiggyCoin/PiggyCore,williamcotton/bitcore,genecyber/bitcore,litecoin-project/litecore,bitjson/bitcore,initaldk/bitcore,janko33bd/bitcore,braydonf/bitcore,maraoz/coinforge,GroestlCoin/groestlcore,phplaboratory/bitcore,adjoinant/bitcore,UdjinM6/bitcore-dash,iobond/bitcore,martindale/bitcore,eXcomm/bitcore,braydonf/bitcore,olalonde/bitcore,eordano/bitcore,martindale/bitcore,williamcotton/bitcore,jcvernaleo/bitcore,initaldk/bitcore,pnagurny/bitcore,iobond/bitcore,MonetaryUnit/bitcore,phplaboratory/bitcore,eXcomm/bitcore,martindale/bitcore,bitpay/bitcore,bankonme/bitcore,janko33bd/bitcore,daxxog/clamcore,jcvernaleo/bitcore,bitpay/bitcore