doc: recommend `--disable-external-signer` in OpenBSD build guide
doc: recommend `--disable-external-signer` in OpenBSD build guide

apoelstra/bitcoin,instagibbs/bitcoin,fanquake/bitcoin,bitcoinknots/bitcoin,prusnak/bitcoin,sstone/bitcoin,AkioNak/bitcoin,mm-s/bitcoin,sipsorcery/bitcoin,bitcoin/bitcoin,namecoin/namecore,bitcoinsSG/bitcoin,AkioNak/bitcoin,yenliangl/bitcoin,GroestlCoin/bitcoin,mm-s/bitcoin,prusnak/bitcoin,anditto/bitcoin,fanquake/bitcoin,bitcoin/bitcoin,ElementsProject/elements,GroestlCoin/GroestlCoin,dscotese/bitcoin,mm-s/bitcoin,ElementsProject/elements,domob1812/bitcoin,bitcoinsSG/bitcoin,jamesob/bitcoin,domob1812/namecore,lateminer/bitcoin,mm-s/bitcoin,bitcoinsSG/bitcoin,kallewoof/bitcoin,mruddy/bitcoin,andreaskern/bitcoin,mruddy/bitcoin,GroestlCoin/GroestlCoin,mruddy/bitcoin,dscotese/bitcoin,yenliangl/bitcoin,particl/particl-core,anditto/bitcoin,Xekyo/bitcoin,JeremyRubin/bitcoin,MarcoFalke/bitcoin,achow101/bitcoin,yenliangl/bitcoin,bitcoinknots/bitcoin,fujicoin/fujicoin,lateminer/bitcoin,jambolo/bitcoin,jambolo/bitcoin,jlopp/statoshi,lateminer/bitcoin,jamesob/bitcoin,ajtowns/bitcoin,tecnovert/particl-core,andreaskern/bitcoin,achow101/bitcoin,Xekyo/bitcoin,namecoin/namecoin-core,Xekyo/bitcoin,dscotese/bitcoin,tecnovert/particl-core,bitcoinsSG/bitcoin,prusnak/bitcoin,MarcoFalke/bitcoin,instagibbs/bitcoin,bitcoinsSG/bitcoin,fujicoin/fujicoin,tecnovert/particl-core,bitcoinknots/bitcoin,instagibbs/bitcoin,achow101/bitcoin,bitcoin/bitcoin,JeremyRubin/bitcoin,bitcoin/bitcoin,qtumproject/qtum,pataquets/namecoin-core,fujicoin/fujicoin,jamesob/bitcoin,domob1812/namecore,namecoin/namecoin-core,prusnak/bitcoin,domob1812/bitcoin,sstone/bitcoin,jambolo/bitcoin,namecoin/namecore,lateminer/bitcoin,sipsorcery/bitcoin,instagibbs/bitcoin,fujicoin/fujicoin,jlopp/statoshi,qtumproject/qtum,bitcoinsSG/bitcoin,sstone/bitcoin,domob1812/bitcoin,pataquets/namecoin-core,JeremyRubin/bitcoin,sipsorcery/bitcoin,sstone/bitcoin,namecoin/namecore,sstone/bitcoin,ElementsProject/elements,bitcoin/bitcoin,achow101/bitcoin,MarcoFalke/bitcoin,anditto/bitcoin,ajtowns/bitcoin,domob1812/namecore,ajtowns/bitcoin,ElementsProject/elements,apoelstra/bitcoin,AkioNak/bitcoin,JeremyRubin/bitcoin,namecoin/namecore,sipsorcery/bitcoin,pataquets/namecoin-core,GroestlCoin/bitcoin,particl/particl-core,mm-s/bitcoin,domob1812/bitcoin,apoelstra/bitcoin,instagibbs/bitcoin,jamesob/bitcoin,bitcoin/bitcoin,bitcoinknots/bitcoin,dscotese/bitcoin,jlopp/statoshi,domob1812/namecore,GroestlCoin/bitcoin,JeremyRubin/bitcoin,domob1812/bitcoin,prusnak/bitcoin,AkioNak/bitcoin,ajtowns/bitcoin,andreaskern/bitcoin,ElementsProject/elements,yenliangl/bitcoin,apoelstra/bitcoin,ElementsProject/elements,Xekyo/bitcoin,qtumproject/qtum,andreaskern/bitcoin,MarcoFalke/bitcoin,JeremyRubin/bitcoin,namecoin/namecore,anditto/bitcoin,pataquets/namecoin-core,particl/particl-core,anditto/bitcoin,lateminer/bitcoin,namecoin/namecoin-core,fanquake/bitcoin,jambolo/bitcoin,domob1812/namecore,jlopp/statoshi,kallewoof/bitcoin,fujicoin/fujicoin,GroestlCoin/bitcoin,domob1812/namecore,namecoin/namecore,mruddy/bitcoin,MarcoFalke/bitcoin,particl/particl-core,namecoin/namecoin-core,apoelstra/bitcoin,mm-s/bitcoin,jambolo/bitcoin,dscotese/bitcoin,bitcoinknots/bitcoin,jlopp/statoshi,AkioNak/bitcoin,namecoin/namecoin-core,particl/particl-core,domob1812/bitcoin,kallewoof/bitcoin,tecnovert/particl-core,particl/particl-core,qtumproject/qtum,jambolo/bitcoin,Xekyo/bitcoin,andreaskern/bitcoin,mruddy/bitcoin,anditto/bitcoin,GroestlCoin/bitcoin,tecnovert/particl-core,instagibbs/bitcoin,ajtowns/bitcoin,GroestlCoin/GroestlCoin,kallewoof/bitcoin,namecoin/namecoin-core,tecnovert/particl-core,lateminer/bitcoin,dscotese/bitcoin,GroestlCoin/GroestlCoin,achow101/bitcoin,qtumproject/qtum,kallewoof/bitcoin,sipsorcery/bitcoin,qtumproject/qtum,fanquake/bitcoin,sstone/bitcoin,fanquake/bitcoin,fanquake/bitcoin,qtumproject/qtum,jlopp/statoshi,GroestlCoin/bitcoin,yenliangl/bitcoin,yenliangl/bitcoin,jamesob/bitcoin,andreaskern/bitcoin,pataquets/namecoin-core,ajtowns/bitcoin,prusnak/bitcoin,AkioNak/bitcoin,mruddy/bitcoin,MarcoFalke/bitcoin,jamesob/bitcoin,fujicoin/fujicoin,kallewoof/bitcoin,GroestlCoin/GroestlCoin,apoelstra/bitcoin,pataquets/namecoin-core,GroestlCoin/GroestlCoin,sipsorcery/bitcoin,Xekyo/bitcoin,achow101/bitcoin