hot and dirty fix for xdggs decode error (#26)

Author: benbovy

docs/earth/xdggs.md

@@ -46,6 +46,27 @@ ds = xdggs.tutorial.open_dataset("air_temperature", "healpix")
 ds
 ```
 
+```{code-cell} python
+---
+tags: [remove-cell]
+---
+from xdggs.utils import GRID_REGISTRY, _extract_cell_id_variable
+
+def from_variables_patch(variables, *, options):
+    _, var, _ = _extract_cell_id_variable(variables)
+
+    grid_name = var.attrs["grid_name"]
+    cls = GRID_REGISTRY.get(grid_name)
+    if cls is None:
+        raise ValueError(f"unknown DGGS grid name: {grid_name}")
+
+    obj = cls.from_variables(variables, options=options)
+    obj._pd_index.index.name = "cell_ids"
+    return obj
+
+xdggs.DGGSIndex.from_variables = from_variables_patch
+```
+
 with that, we can decode the metadata:
 
 ```{code-cell} python