doc: Document -checklevel levels
doc: Document -checklevel levels

Document the various possible check levels for the command-line
argument. The numbers say nothing on their own.

RHavar/bitcoin,rnicoll/bitcoin,particl/particl-core,vertcoin/vertcoin,peercoin/peercoin,rnicoll/bitcoin,CryptArc/bitcoin,alecalve/bitcoin,kazcw/bitcoin,GlobalBoost/GlobalBoost,GlobalBoost/GlobalBoost,Xekyo/bitcoin,practicalswift/bitcoin,JeremyRubin/bitcoin,cdecker/bitcoin,GroestlCoin/bitcoin,prusnak/bitcoin,wellenreiter01/Feathercoin,prusnak/bitcoin,droark/bitcoin,EthanHeilman/bitcoin,tjps/bitcoin,bitcoin/bitcoin,bitcoinknots/bitcoin,practicalswift/bitcoin,bespike/litecoin,MarcoFalke/bitcoin,droark/bitcoin,practicalswift/bitcoin,instagibbs/bitcoin,FeatherCoin/Feathercoin,instagibbs/bitcoin,kazcw/bitcoin,alecalve/bitcoin,wellenreiter01/Feathercoin,gjhiggins/vcoincore,DigitalPandacoin/pandacoin,OmniLayer/omnicore,Christewart/bitcoin,Kogser/bitcoin,dscotese/bitcoin,rnicoll/bitcoin,untrustbank/litecoin,r8921039/bitcoin,namecoin/namecoin-core,myriadcoin/myriadcoin,apoelstra/bitcoin,ahmedbodi/vertcoin,GlobalBoost/GlobalBoost,midnightmagic/bitcoin,tecnovert/particl-core,ahmedbodi/vertcoin,GlobalBoost/GlobalBoost,GroestlCoin/bitcoin,EthanHeilman/bitcoin,cdecker/bitcoin,untrustbank/litecoin,achow101/bitcoin,Xekyo/bitcoin,Xekyo/bitcoin,vertcoin/vertcoin,domob1812/bitcoin,jnewbery/bitcoin,qtumproject/qtum,n1bor/bitcoin,apoelstra/bitcoin,jnewbery/bitcoin,andreaskern/bitcoin,GlobalBoost/GlobalBoost,GroestlCoin/bitcoin,EthanHeilman/bitcoin,Sjors/bitcoin,domob1812/namecore,bitcoinsSG/bitcoin,mm-s/bitcoin,GroestlCoin/GroestlCoin,qtumproject/qtum,r8921039/bitcoin,domob1812/namecore,tecnovert/particl-core,ElementsProject/elements,MarcoFalke/bitcoin,jambolo/bitcoin,JeremyRubin/bitcoin,mm-s/bitcoin,litecoin-project/litecoin,namecoin/namecoin-core,nikkitan/bitcoin,fujicoin/fujicoin,jamesob/bitcoin,Kogser/bitcoin,gjhiggins/vcoincore,mruddy/bitcoin,alecalve/bitcoin,nikkitan/bitcoin,mm-s/bitcoin,ElementsProject/elements,jambolo/bitcoin,fujicoin/fujicoin,lateminer/bitcoin,mruddy/bitcoin,ahmedbodi/vertcoin,rnicoll/dogecoin,afk11/bitcoin,RHavar/bitcoin,particl/particl-core,n1bor/bitcoin,jtimon/bitcoin,cdecker/bitcoin,gjhiggins/vcoincore,GroestlCoin/GroestlCoin,alecalve/bitcoin,mruddy/bitcoin,CryptArc/bitcoin,myriadteam/myriadcoin,yenliangl/bitcoin,prusnak/bitcoin,Kogser/bitcoin,domob1812/namecore,MarcoFalke/bitcoin,tjps/bitcoin,myriadcoin/myriadcoin,jambolo/bitcoin,myriadcoin/myriadcoin,ajtowns/bitcoin,rnicoll/dogecoin,andreaskern/bitcoin,sstone/bitcoin,fanquake/bitcoin,mm-s/bitcoin,dscotese/bitcoin,apoelstra/bitcoin,Sjors/bitcoin,monacoinproject/monacoin,AkioNak/bitcoin,afk11/bitcoin,r8921039/bitcoin,untrustbank/litecoin,nikkitan/bitcoin,CryptArc/bitcoin,sstone/bitcoin,tecnovert/particl-core,achow101/bitcoin,Christewart/bitcoin,untrustbank/litecoin,ajtowns/bitcoin,peercoin/peercoin,untrustbank/litecoin,GroestlCoin/GroestlCoin,anditto/bitcoin,kallewoof/bitcoin,FeatherCoin/Feathercoin,gjhiggins/vcoincore,midnightmagic/bitcoin,jambolo/bitcoin,ElementsProject/elements,RHavar/bitcoin,mitchellcash/bitcoin,jamesob/bitcoin,practicalswift/bitcoin,prusnak/bitcoin,JeremyRubin/bitcoin,particl/particl-core,bitcoin/bitcoin,ericshawlinux/bitcoin,qtumproject/qtum,jtimon/bitcoin,MeshCollider/bitcoin,ajtowns/bitcoin,JeremyRubin/bitcoin,wellenreiter01/Feathercoin,Kogser/bitcoin,prusnak/bitcoin,litecoin-project/litecoin,domob1812/namecore,domob1812/bitcoin,sipsorcery/bitcoin,sipsorcery/bitcoin,bitcoinsSG/bitcoin,lateminer/bitcoin,ahmedbodi/vertcoin,domob1812/namecore,peercoin/peercoin,mruddy/bitcoin,achow101/bitcoin,yenliangl/bitcoin,ericshawlinux/bitcoin,mm-s/bitcoin,AkioNak/bitcoin,bitcoinsSG/bitcoin,andreaskern/bitcoin,jnewbery/bitcoin,midnightmagic/bitcoin,rnicoll/bitcoin,RHavar/bitcoin,bitcoin/bitcoin,instagibbs/bitcoin,FeatherCoin/Feathercoin,tecnovert/particl-core,andreaskern/bitcoin,pataquets/namecoin-core,nikkitan/bitcoin,instagibbs/bitcoin,r8921039/bitcoin,tjps/bitcoin,namecoin/namecore,anditto/bitcoin,afk11/bitcoin,afk11/bitcoin,pstratem/bitcoin,Sjors/bitcoin,GroestlCoin/GroestlCoin,vertcoin/vertcoin,r8921039/bitcoin,droark/bitcoin,MeshCollider/bitcoin,mruddy/bitcoin,vertcoin/vertcoin,Kogser/bitcoin,cdecker/bitcoin,jamesob/bitcoin,Kogser/bitcoin,jlopp/statoshi,rnicoll/dogecoin,monacoinproject/monacoin,mitchellcash/bitcoin,myriadteam/myriadcoin,OmniLayer/omnicore,gjhiggins/vcoincore,OmniLayer/omnicore,mruddy/bitcoin,afk11/bitcoin,myriadteam/myriadcoin,ajtowns/bitcoin,monacoinproject/monacoin,JeremyRubin/bitcoin,fanquake/bitcoin,bitcoinknots/bitcoin,DigitalPandacoin/pandacoin,peercoin/peercoin,jlopp/statoshi,myriadcoin/myriadcoin,bitcoinknots/bitcoin,CryptArc/bitcoin,bitcoinknots/bitcoin,GroestlCoin/GroestlCoin,EthanHeilman/bitcoin,domob1812/bitcoin,midnightmagic/bitcoin,namecoin/namecore,fanquake/bitcoin,pataquets/namecoin-core,pataquets/namecoin-core,namecoin/namecore,practicalswift/bitcoin,OmniLayer/omnicore,yenliangl/bitcoin,DigitalPandacoin/pandacoin,RHavar/bitcoin,MeshCollider/bitcoin,jamesob/bitcoin,jtimon/bitcoin,jnewbery/bitcoin,ahmedbodi/vertcoin,litecoin-project/litecoin,pstratem/bitcoin,bitcoinsSG/bitcoin,namecoin/namecoin-core,domob1812/namecore,bitcoinsSG/bitcoin,kallewoof/bitcoin,lateminer/bitcoin,monacoinproject/monacoin,particl/particl-core,Christewart/bitcoin,particl/particl-core,prusnak/bitcoin,DigitalPandacoin/pandacoin,andreaskern/bitcoin,namecoin/namecoin-core,tecnovert/particl-core,namecoin/namecore,namecoin/namecore,vertcoin/vertcoin,bitcoinsSG/bitcoin,jamesob/bitcoin,mitchellcash/bitcoin,wellenreiter01/Feathercoin,myriadteam/myriadcoin,jtimon/bitcoin,bespike/litecoin,myriadteam/myriadcoin,domob1812/bitcoin,AkioNak/bitcoin,OmniLayer/omnicore,Kogser/bitcoin,anditto/bitcoin,MarcoFalke/bitcoin,ericshawlinux/bitcoin,qtumproject/qtum,monacoinproject/monacoin,domob1812/bitcoin,tjps/bitcoin,yenliangl/bitcoin,Kogser/bitcoin,Kogser/bitcoin,pstratem/bitcoin,pstratem/bitcoin,CryptArc/bitcoin,andreaskern/bitcoin,kazcw/bitcoin,MeshCollider/bitcoin,gjhiggins/vcoincore,jamesob/bitcoin,mitchellcash/bitcoin,ajtowns/bitcoin,apoelstra/bitcoin,JeremyRubin/bitcoin,practicalswift/bitcoin,alecalve/bitcoin,dscotese/bitcoin,AkioNak/bitcoin,achow101/bitcoin,sstone/bitcoin,jambolo/bitcoin,achow101/bitcoin,GroestlCoin/bitcoin,yenliangl/bitcoin,pataquets/namecoin-core,kallewoof/bitcoin,instagibbs/bitcoin,Kogser/bitcoin,Christewart/bitcoin,lateminer/bitcoin,n1bor/bitcoin,sstone/bitcoin,bespike/litecoin,myriadteam/myriadcoin,Kogser/bitcoin,DigitalPandacoin/pandacoin,CryptArc/bitcoin,droark/bitcoin,FeatherCoin/Feathercoin,untrustbank/litecoin,vertcoin/vertcoin,droark/bitcoin,alecalve/bitcoin,ericshawlinux/bitcoin,tjps/bitcoin,MarcoFalke/bitcoin,ericshawlinux/bitcoin,MarcoFalke/bitcoin,anditto/bitcoin,jlopp/statoshi,bitcoinknots/bitcoin,rnicoll/dogecoin,dscotese/bitcoin,GroestlCoin/GroestlCoin,fanquake/bitcoin,Christewart/bitcoin,n1bor/bitcoin,nikkitan/bitcoin,midnightmagic/bitcoin,bespike/litecoin,jtimon/bitcoin,GroestlCoin/bitcoin,achow101/bitcoin,qtumproject/qtum,Christewart/bitcoin,ajtowns/bitcoin,fanquake/bitcoin,FeatherCoin/Feathercoin,MeshCollider/bitcoin,GlobalBoost/GlobalBoost,anditto/bitcoin,GroestlCoin/bitcoin,jambolo/bitcoin,particl/particl-core,mm-s/bitcoin,nikkitan/bitcoin,jonasschnelli/bitcoin,ahmedbodi/vertcoin,AkioNak/bitcoin,kazcw/bitcoin,litecoin-project/litecoin,sipsorcery/bitcoin,Sjors/bitcoin,namecoin/namecoin-core,RHavar/bitcoin,MeshCollider/bitcoin,sstone/bitcoin,bitcoin/bitcoin,wellenreiter01/Feathercoin,rnicoll/dogecoin,OmniLayer/omnicore,lateminer/bitcoin,ElementsProject/elements,monacoinproject/monacoin,myriadcoin/myriadcoin,sipsorcery/bitcoin,fanquake/bitcoin,GlobalBoost/GlobalBoost,fujicoin/fujicoin,wellenreiter01/Feathercoin,fujicoin/fujicoin,Xekyo/bitcoin,Sjors/bitcoin,mitchellcash/bitcoin,mitchellcash/bitcoin,kallewoof/bitcoin,lateminer/bitcoin,tjps/bitcoin,n1bor/bitcoin,domob1812/bitcoin,apoelstra/bitcoin,jlopp/statoshi,jonasschnelli/bitcoin,jonasschnelli/bitcoin,kazcw/bitcoin,Xekyo/bitcoin,Xekyo/bitcoin,pstratem/bitcoin,sstone/bitcoin,ElementsProject/elements,sipsorcery/bitcoin,ericshawlinux/bitcoin,droark/bitcoin,jonasschnelli/bitcoin,jtimon/bitcoin,n1bor/bitcoin,pataquets/namecoin-core,EthanHeilman/bitcoin,jlopp/statoshi,qtumproject/qtum,jnewbery/bitcoin,kallewoof/bitcoin,AkioNak/bitcoin,fujicoin/fujicoin,yenliangl/bitcoin,fujicoin/fujicoin,cdecker/bitcoin,litecoin-project/litecoin,namecoin/namecoin-core,qtumproject/qtum,apoelstra/bitcoin,kallewoof/bitcoin,rnicoll/bitcoin,sipsorcery/bitcoin,anditto/bitcoin,afk11/bitcoin,dscotese/bitcoin,FeatherCoin/Feathercoin,cdecker/bitcoin,dscotese/bitcoin,litecoin-project/litecoin,jonasschnelli/bitcoin,tecnovert/particl-core,bespike/litecoin,peercoin/peercoin,instagibbs/bitcoin,pataquets/namecoin-core,bespike/litecoin,bitcoin/bitcoin,peercoin/peercoin,kazcw/bitcoin,r8921039/bitcoin,pstratem/bitcoin,bitcoin/bitcoin,jlopp/statoshi,DigitalPandacoin/pandacoin,midnightmagic/bitcoin,namecoin/namecore,ElementsProject/elements,rnicoll/bitcoin,myriadcoin/myriadcoin,Kogser/bitcoin,EthanHeilman/bitcoin