Documentation on adding tile layers

Is there any documentation on how to add a tile layer to the map?

have tried 

```python
M.add_layer("layername","http://tiles{0-3}.basemap.com/url/{z}/{x}/{y}.png")
```
But it looks like the layer that gets added is requesting:
`http://localhost:8888/notebooks/notebooks/null/9/8/4.png` etc