New section to link from longhand to shorthand property

## What is the new suggestion?

for example

at page https://developer.mozilla.org/en-US/docs/Web/CSS/place-content
show, `place-content` is a shorthand for `align-content` and `justify-content`

Can you do something like that,
at https://developer.mozilla.org/en-US/docs/Web/CSS/align-content
and https://developer.mozilla.org/en-US/docs/Web/CSS/justify-content page,
show They have this `place-content` shorthand.

I think this will useful.thanks.

## Why is it important or useful?

## Other supporting information