Update README to be more clear about DB migrations
Update README to be more clear about DB migrations

CulturePlex/pybossa,geotagx/pybossa,Scifabric/pybossa,geotagx/geotagx-pybossa-archive,geotagx/geotagx-pybossa-archive,PyBossa/pybossa,OpenNewsLabs/pybossa,PyBossa/pybossa,inteligencia-coletiva-lsd/pybossa,harihpr/tweetclickers,jean/pybossa,proyectos-analizo-info/pybossa-analizo-info,OpenNewsLabs/pybossa,geotagx/geotagx-pybossa-archive,CulturePlex/pybossa,geotagx/geotagx-pybossa-archive,harihpr/tweetclickers,geotagx/geotagx-pybossa-archive,Scifabric/pybossa,stefanhahmann/pybossa,jean/pybossa,geotagx/pybossa,stefanhahmann/pybossa,CulturePlex/pybossa,proyectos-analizo-info/pybossa-analizo-info,proyectos-analizo-info/pybossa-analizo-info,inteligencia-coletiva-lsd/pybossa