Documentation says `grid_mapping` is in attrs but really is in `encoding`

[arkanoid87]

I was handling missing CRS information in my Zarr files, but I was dealing with a missing grid_mapping in attrs when it really was in encoding.

CRS Management page says Look in attributes (attrs) of your data array for the grid_mapping coordinate name.

but the API says it's in encoding

[snowman2]

A PR updating the documentation is welcome.

[snowman2]

encoding is the correct location