add a few build notes to the README for us poor windows sods
add a few build notes to the README for us poor windows sods

ISNIT0/ractive,marcalexiei/ractive,pingjiang/ractive,marcalexiei/ractive,marcalexiei/ractive,heavyk/ractive,thomsbg/ractive,pingjiang/ractive,ISNIT0/ractive,JonDum/ractive,heavyk/ractive,pingjiang/ractive,magicdawn/ractive,dyx/ractive,ISNIT0/ractive,JonDum/ractive,cgvarela/ractive,ractivejs/ractive,ractivejs/ractive,dyx/ractive,ndimas/ractive,squaredup/ractive,Rich-Harris/ractive,ndimas/ractive,heavyk/ractive,magicdawn/ractive,cgvarela/ractive,JonDum/ractive,thomsbg/ractive,cgvarela/ractive,aliprogrammer69/ractive,magicdawn/ractive,squaredup/ractive,aliprogrammer69/ractive,Rich-Harris/ractive,aliprogrammer69/ractive,dyx/ractive,squaredup/ractive,Rich-Harris/ractive,ractivejs/ractive,ndimas/ractive,thomsbg/ractive