Added README notes about building on OS X
Added README notes about building on OS X

afh/ledger,paulbdavis/ledger,duncanmortimer/ledger,ledger/ledger,duncanmortimer/ledger,afh/ledger,jwakely/ledger,paulbdavis/ledger,paulbdavis/ledger,duncanmortimer/ledger,jwakely/ledger,ledger/ledger,jwakely/ledger,duncanmortimer/ledger,afh/ledger,ledger/ledger,duncanmortimer/ledger,duncanmortimer/ledger,afh/ledger,paulbdavis/ledger,paulbdavis/ledger,ledger/ledger,jwakely/ledger,jwakely/ledger,paulbdavis/ledger,paulbdavis/ledger,jwakely/ledger,afh/ledger,jwakely/ledger,ledger/ledger,duncanmortimer/ledger