[css-grid-2] Add link for ambiguous reference.

[tiaanl]

There is mention here to "See above" when referencing intrinsic sizing. Up to this point there is not a lot of mention about intrinsic sizing and even the title of the paragraph it is referencing to has no mention of intrinsic sizing. The title only says: "Sizing Grid Containers". A link to the actual paragraph would be much more descriptive here:

https://github.com/w3c/csswg-drafts/blob/main/css-grid-2/Overview.bs#L992

Possibly just changing (See above) to (<a>intrinsic-sizes</a>)

[fantasai]

Added a cross-reference, thanks for the suggestion!