Fixed issues in README and documentation

migrate.go

@@ -29,7 +29,8 @@ const fileFormat = `%04d.sql`
 // AssetFunc is a function that returns the data for the given name
 type AssetFunc func(string) ([]byte, error)
 
-// Migrate executes
+// Migrate executes migrations to get to the desired version
+// Downgrading is not supported as it could result in data loss
 func Migrate(db *sql.DB, version int, o Options, asset AssetFunc) error {
 	if o.TableName == `` {
 		o.TableName = DefaultTableName