Adds Android docs to landing page
Adds Android docs to landing page

Summary: Adds a simple "photo with poster and comment" layout to the landing page as an example for Android, along with the XML.

Reviewed By: emilsjolander

Differential Revision: D4558478

fbshipit-source-id: c7302321a67e99f5853358e711ff538d192f06e9

facebook/yoga,facebook/yoga,facebook/css-layout,yihuang/css-layout,facebook/yoga,facebook/css-layout,facebook/yoga,yihuang/css-layout,yihuang/css-layout,facebook/css-layout,rmarinho/yoga,rmarinho/yoga,facebook/yoga,yihuang/css-layout,rmarinho/yoga,rmarinho/yoga,yihuang/css-layout,rmarinho/yoga,yihuang/css-layout,facebook/css-layout,rmarinho/yoga,rmarinho/yoga,facebook/yoga,facebook/css-layout,yihuang/css-layout,facebook/css-layout,facebook/yoga,yihuang/css-layout,facebook/yoga,yihuang/css-layout,facebook/css-layout,rmarinho/yoga,facebook/yoga,yihuang/css-layout,facebook/css-layout,rmarinho/yoga,rmarinho/yoga,facebook/css-layout,facebook/yoga