Clarify __matmul__ does generalized dot product (pydata#9060)

doc/user-guide/computation.rst

@@ -50,7 +50,7 @@ Use :py:func:`~xarray.where` to conditionally switch between values:
 
     xr.where(arr > 0, "positive", "negative")
 
-Use `@` to perform matrix multiplication:
+Use `@` to compute the :py:func:`~xarray.dot` product:
 
 .. ipython:: python