create a documentation for config path

docs/sanic/config.md

@@ -53,6 +53,15 @@ import myapp.default_settings
 app = Sanic('myapp')
 app.config.from_object(myapp.default_settings)
 ```
+or also by path to config:
+
+```
+import myapp.default_settings
+
+app = Sanic('myapp')
+app.config.from_object('config.path.config.Class')
+```
+
 
 You could use a class or any other object as well.
 

tests/test_config.py

@@ -16,17 +16,25 @@ def temp_path():
         yield Path(td, 'file')
 
 
-def test_load_from_object(app):
-    class Config:
+class Config:
         not_for_config = 'should not be used'
         CONFIG_VALUE = 'should be used'
 
+
+def test_load_from_object(app):
     app.config.from_object(Config)
     assert 'CONFIG_VALUE' in app.config
     assert app.config.CONFIG_VALUE == 'should be used'
     assert 'not_for_config' not in app.config
 
 
+def test_load_from_object_string(app):
+    app.config.from_object('test_config.Config')
+    assert 'CONFIG_VALUE' in app.config
+    assert app.config.CONFIG_VALUE == 'should be used'
+    assert 'not_for_config' not in app.config
+
+
 def test_auto_load_env():
     environ["SANIC_TEST_ANSWER"] = "42"
     app = Sanic()