Update build information
Update build information

Add the command necessary to add ppa repository in Ubuntu

Refs #3757

Infernoman/crowncoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,domob1812/crowncoin,Infernoman/crowncoin,domob1812/crowncoin,Crowndev/crowncoin,syscoin/syscoin,Crowndev/crowncoin,syscoin/syscoin,Crowndev/crowncoin,domob1812/crowncoin,syscoin/syscoin,Infernoman/crowncoin,Crowndev/crowncoin,Infernoman/crowncoin,syscoin/syscoin,syscoin/syscoin,Crowndev/crowncoin,domob1812/crowncoin,domob1812/crowncoin,Infernoman/crowncoin,domob1812/crowncoin,Infernoman/crowncoin,Crowndev/crowncoin