Raising error on missing configuration file inclusion

beets/__init__.py

@@ -35,6 +35,8 @@ class IncludeLazyConfig(confuse.LazyConfig):
                 filename = view.as_filename()
                 if os.path.isfile(filename):
                     self.set_file(filename)
+                else:
+                    raise FileNotFoundError("Warning! Configuration file({0}) does not exist!".format(filename))
         except confuse.NotFoundError:
             pass