Fix typo in docs
Fix typo in docs

Summary:
"feature" should be "features" but it's already used twice in that paragraph so
I replaced it with "showcases" instead.

Reviewed By: emilsjolander

Differential Revision: D7042770

fbshipit-source-id: 0287f8746feca5c9f651950c8e9c24d2e86d55e9

facebook/css-layout,facebook/yoga,facebook/css-layout,facebook/yoga,facebook/css-layout,facebook/css-layout,facebook/css-layout,facebook/yoga,facebook/yoga,facebook/yoga,facebook/yoga,facebook/css-layout,facebook/yoga,facebook/yoga,facebook/yoga,facebook/css-layout,facebook/css-layout,facebook/yoga,facebook/css-layout