Provide shape info in shape mismatch error. (#3619)

* Provide shape info in shape mismatch error.

* Reword error message.

Co-Authored-By: Deepak Cherian <dcherian@users.noreply.github.com>

Author: danielballan

xarray/core/variable.py

@@ -346,7 +346,10 @@ def data(self):
     def data(self, data):
         data = as_compatible_data(data)
         if data.shape != self.shape:
-            raise ValueError("replacement data must match the Variable's shape")
+            raise ValueError(
+                f"replacement data must match the Variable's shape. "
+                f"replacement data has shape {data.shape}; Variable has shape {self.shape}"
+            )
         self._data = data
 
     def load(self, **kwargs):