ion-skeleton-text usage missing

[chrisgriffith]

It seems the usage pane is missing, along with a sample app.
https://ionicframework.com/docs/api/skeleton-text

[camwiegert]

Looks like this happened because we have a usage example, but it's empty.

[brandyscarney]

I've added this as part of this PR: ionic-team/ionic-framework#17612

Note that some of the usage examples will not work perfectly without my PR. 🙂

[fahimehahmadi94]

ion-skeleton-text {
--background-rgb: 230,40,50;
}