update checkout customization guide mentioning need to register custom Checkout states with CheckoutsController to avoid no method error
update checkout customization guide mentioning need to register custom Checkout states with CheckoutsController to avoid no method error

vulk/spree,AgilTec/spree,reidblomquist/spree,wolfieorama/spree,wolfieorama/spree,dandanwei/spree,maybii/spree,karlitxo/spree,Migweld/spree,reinaris/spree,ayb/spree,rbngzlv/spree,PhoenixTeam/spree_phoenix,ramkumar-kr/spree,welitonfreitas/spree,reidblomquist/spree,groundctrl/spree,agient/agientstorefront,shekibobo/spree,nooysters/spree,NerdsvilleCEO/spree,kewaunited/spree,trigrass2/spree,sunny2601/spree,sliaquat/spree,wolfieorama/spree,Hawaiideveloper/shoppingcart,reinaris/spree,surfdome/spree,FadliKun/spree,ujai/spree,degica/spree,shaywood2/spree,assembledbrands/spree,robodisco/spree,beni55/spree,yiqing95/spree,APohio/spree,dandanwei/spree,DarkoP/spree,maybii/spree,robodisco/spree,xuewenfei/solidus,moneyspyder/spree,jasonfb/spree,moneyspyder/spree,Migweld/spree,jordan-brough/solidus,rakibulislam/spree,agient/agientstorefront,net2b/spree,groundctrl/spree,shaywood2/spree,SadTreeFriends/spree,hoanghiep90/spree,azclick/spree,vinsol/spree,jasonfb/spree,camelmasa/spree,derekluo/spree,fahidnasir/spree,TrialGuides/spree,sideci-sample/sideci-sample-spree,rajeevriitm/spree,CJMrozek/spree,caiqinghua/spree,dandanwei/spree,siddharth28/spree,JuandGirald/spree,bonobos/solidus,jordan-brough/solidus,sunny2601/spree,azranel/spree,delphsoft/spree-store-ballchair,sliaquat/spree,athal7/solidus,alvinjean/spree,kewaunited/spree,thogg4/spree,APohio/spree,Hawaiideveloper/shoppingcart,shekibobo/spree,jaspreet21anand/spree,keatonrow/spree,ckk-scratch/solidus,vcavallo/spree,lyzxsc/spree,alejandromangione/spree,azranel/spree,grzlus/spree,alejandromangione/spree,JuandGirald/spree,mindvolt/spree,mindvolt/spree,progsri/spree,jparr/spree,omarsar/spree,dafontaine/spree,Senjai/solidus,xuewenfei/solidus,zamiang/spree,agient/agientstorefront,edgward/spree,ahmetabdi/spree,tancnle/spree,edgward/spree,shekibobo/spree,orenf/spree,pervino/spree,beni55/spree,karlitxo/spree,jsurdilla/solidus,vcavallo/spree,shekibobo/spree,CiscoCloud/spree,lsirivong/solidus,softr8/spree,yushine/spree,degica/spree,forkata/solidus,TrialGuides/spree,thogg4/spree,NerdsvilleCEO/spree,Ropeney/spree,keatonrow/spree,bricesanchez/spree,softr8/spree,CiscoCloud/spree,pervino/spree,sliaquat/spree,rbngzlv/spree,ckk-scratch/solidus,omarsar/spree,miyazawatomoka/spree,alvinjean/spree,njerrywerry/spree,Boomkat/spree,joanblake/spree,Machpowersystems/spree_mach,cutefrank/spree,calvinl/spree,JDutil/spree,jimblesm/spree,tomash/spree,priyank-gupta/spree,berkes/spree,azclick/spree,mindvolt/spree,brchristian/spree,brchristian/spree,xuewenfei/solidus,tomash/spree,AgilTec/spree,Kagetsuki/spree,grzlus/spree,Lostmyname/spree,AgilTec/spree,devilcoders/solidus,PhoenixTeam/spree_phoenix,joanblake/spree,brchristian/spree,rakibulislam/spree,dafontaine/spree,vinsol/spree,ramkumar-kr/spree,carlesjove/spree,derekluo/spree,wolfieorama/spree,hoanghiep90/spree,sfcgeorge/spree,sliaquat/spree,azranel/spree,FadliKun/spree,Arpsara/solidus,jsurdilla/solidus,abhishekjain16/spree,surfdome/spree,JuandGirald/spree,sfcgeorge/spree,forkata/solidus,trigrass2/spree,delphsoft/spree-store-ballchair,TimurTarasenko/spree,patdec/spree,dafontaine/spree,TrialGuides/spree,progsri/spree,cutefrank/spree,tesserakt/clean_spree,fahidnasir/spree,JuandGirald/spree,xuewenfei/solidus,odk211/spree,jaspreet21anand/spree,tomash/spree,priyank-gupta/spree,carlesjove/spree,azclick/spree,reinaris/spree,archSeer/spree,jasonfb/spree,volpejoaquin/spree,priyank-gupta/spree,vinayvinsol/spree,camelmasa/spree,yiqing95/spree,SadTreeFriends/spree,lsirivong/solidus,odk211/spree,richardnuno/solidus,madetech/spree,fahidnasir/spree,welitonfreitas/spree,trigrass2/spree,NerdsvilleCEO/spree,tancnle/spree,yiqing95/spree,jparr/spree,CJMrozek/spree,tesserakt/clean_spree,PhoenixTeam/spree_phoenix,rajeevriitm/spree,berkes/spree,rbngzlv/spree,JDutil/spree,scottcrawford03/solidus,jsurdilla/solidus,richardnuno/solidus,pervino/spree,adaddeo/spree,pulkit21/spree,archSeer/spree,vmatekole/spree,raow/spree,radarseesradar/spree,jordan-brough/solidus,pervino/solidus,derekluo/spree,gautamsawhney/spree,rbngzlv/spree,softr8/spree,Senjai/solidus,adaddeo/spree,hifly/spree,locomotivapro/spree,pervino/spree,Ropeney/spree,joanblake/spree,gautamsawhney/spree,carlesjove/spree,Engeltj/spree,kewaunited/spree,alvinjean/spree,lsirivong/spree,orenf/spree,ayb/spree,ramkumar-kr/spree,mleglise/spree,jasonfb/spree,jeffboulet/spree,scottcrawford03/solidus,Machpowersystems/spree_mach,raow/spree,locomotivapro/spree,ujai/spree,edgward/spree,camelmasa/spree,forkata/solidus,CiscoCloud/spree,athal7/solidus,CJMrozek/spree,alejandromangione/spree,scottcrawford03/solidus,project-eutopia/spree,jspizziri/spree,JDutil/spree,jimblesm/spree,yushine/spree,ujai/spree,jspizziri/spree,Arpsara/solidus,useiichi/spree,net2b/spree,omarsar/spree,vmatekole/spree,KMikhaylovCTG/spree,scottcrawford03/solidus,madetech/spree,camelmasa/spree,archSeer/spree,mleglise/spree,groundctrl/spree,delphsoft/spree-store-ballchair,alvinjean/spree,net2b/spree,richardnuno/solidus,priyank-gupta/spree,vulk/spree,lyzxsc/spree,JDutil/spree,bricesanchez/spree,TimurTarasenko/spree,adaddeo/spree,trigrass2/spree,vinsol/spree,bricesanchez/spree,imella/spree,Senjai/solidus,DynamoMTL/spree,Kagetsuki/spree,firman/spree,radarseesradar/spree,Ropeney/spree,imella/spree,abhishekjain16/spree,caiqinghua/spree,Lostmyname/spree,dafontaine/spree,builtbybuffalo/spree,jimblesm/spree,vinayvinsol/spree,robodisco/spree,patdec/spree,calvinl/spree,welitonfreitas/spree,sfcgeorge/spree,gregoryrikson/spree-sample,jspizziri/spree,volpejoaquin/spree,keatonrow/spree,groundctrl/spree,siddharth28/spree,FadliKun/spree,jeffboulet/spree,pulkit21/spree,lsirivong/spree,beni55/spree,builtbybuffalo/spree,sfcgeorge/spree,hoanghiep90/spree,project-eutopia/spree,hifly/spree,vulk/spree,quentinuys/spree,Engeltj/spree,patdec/spree,moneyspyder/spree,mindvolt/spree,Boomkat/spree,sunny2601/spree,mleglise/spree,lyzxsc/spree,pervino/solidus,azclick/spree,assembledbrands/spree,moneyspyder/spree,miyazawatomoka/spree,pulkit21/spree,zaeznet/spree,reidblomquist/spree,vmatekole/spree,TrialGuides/spree,karlitxo/spree,useiichi/spree,piousbox/spree,yushine/spree,miyazawatomoka/spree,CiscoCloud/spree,vcavallo/spree,vinsol/spree,gregoryrikson/spree-sample,nooysters/spree,zaeznet/spree,carlesjove/spree,rajeevriitm/spree,robodisco/spree,radarseesradar/spree,gautamsawhney/spree,zamiang/spree,piousbox/spree,zaeznet/spree,ayb/spree,reinaris/spree,firman/spree,madetech/spree,firman/spree,useiichi/spree,FadliKun/spree,Kagetsuki/spree,cutefrank/spree,SadTreeFriends/spree,Lostmyname/spree,berkes/spree,DarkoP/spree,orenf/spree,karlitxo/spree,bonobos/solidus,azranel/spree,vmatekole/spree,volpejoaquin/spree,DarkoP/spree,sideci-sample/sideci-sample-spree,assembledbrands/spree,grzlus/spree,caiqinghua/spree,piousbox/spree,Boomkat/spree,softr8/spree,odk211/spree,yushine/spree,jaspreet21anand/spree,Migweld/spree,calvinl/spree,joanblake/spree,grzlus/spree,project-eutopia/spree,ckk-scratch/solidus,builtbybuffalo/spree,lsirivong/solidus,net2b/spree,shaywood2/spree,nooysters/spree,raow/spree,tomash/spree,maybii/spree,SadTreeFriends/spree,jeffboulet/spree,sideci-sample/sideci-sample-spree,surfdome/spree,orenf/spree,zamiang/spree,maybii/spree,shaywood2/spree,DynamoMTL/spree,jeffboulet/spree,devilcoders/solidus,calvinl/spree,Ropeney/spree,jordan-brough/solidus,ahmetabdi/spree,rajeevriitm/spree,caiqinghua/spree,zamiang/spree,forkata/solidus,Engeltj/spree,grzlus/solidus,jparr/spree,devilcoders/solidus,pulkit21/spree,hoanghiep90/spree,mleglise/spree,nooysters/spree,tesserakt/clean_spree,sunny2601/spree,jsurdilla/solidus,DynamoMTL/spree,thogg4/spree,DarkoP/spree,archSeer/spree,vulk/spree,yiqing95/spree,grzlus/solidus,gregoryrikson/spree-sample,jaspreet21anand/spree,abhishekjain16/spree,njerrywerry/spree,gregoryrikson/spree-sample,project-eutopia/spree,grzlus/solidus,beni55/spree,Boomkat/spree,AgilTec/spree,Migweld/spree,Hawaiideveloper/shoppingcart,tancnle/spree,surfdome/spree,odk211/spree,thogg4/spree,berkes/spree,Machpowersystems/spree_mach,adaddeo/spree,tesserakt/clean_spree,useiichi/spree,CJMrozek/spree,athal7/solidus,devilcoders/solidus,lsirivong/spree,siddharth28/spree,jimblesm/spree,quentinuys/spree,KMikhaylovCTG/spree,bonobos/solidus,piousbox/spree,locomotivapro/spree,ckk-scratch/solidus,Lostmyname/spree,ayb/spree,Hawaiideveloper/shoppingcart,vinayvinsol/spree,vcavallo/spree,pervino/solidus,jparr/spree,edgward/spree,lsirivong/spree,miyazawatomoka/spree,firman/spree,APohio/spree,pervino/solidus,brchristian/spree,welitonfreitas/spree,vinayvinsol/spree,njerrywerry/spree,siddharth28/spree,dandanwei/spree,APohio/spree,agient/agientstorefront,rakibulislam/spree,omarsar/spree,bonobos/solidus,NerdsvilleCEO/spree,quentinuys/spree,Arpsara/solidus,ahmetabdi/spree,grzlus/solidus,ahmetabdi/spree,quentinuys/spree,hifly/spree,lyzxsc/spree,richardnuno/solidus,njerrywerry/spree,radarseesradar/spree,DynamoMTL/spree,TimurTarasenko/spree,keatonrow/spree,gautamsawhney/spree,imella/spree,hifly/spree,progsri/spree,PhoenixTeam/spree_phoenix,kewaunited/spree,Arpsara/solidus,volpejoaquin/spree,zaeznet/spree,delphsoft/spree-store-ballchair,rakibulislam/spree,derekluo/spree,Kagetsuki/spree,KMikhaylovCTG/spree,abhishekjain16/spree,TimurTarasenko/spree,KMikhaylovCTG/spree,degica/spree,fahidnasir/spree,ramkumar-kr/spree,tancnle/spree,patdec/spree,athal7/solidus,jspizziri/spree,progsri/spree,locomotivapro/spree,alejandromangione/spree,reidblomquist/spree,Senjai/solidus,builtbybuffalo/spree,cutefrank/spree,raow/spree,lsirivong/solidus,madetech/spree,Engeltj/spree