added amp-img example with fallback attribute (#10122)
added amp-img example with fallback attribute (#10122)


JeromeFitz/next.js,azukaru/next.js,JeromeFitz/next.js,zeit/next.js,zeit/next.js,flybayer/next.js,flybayer/next.js,azukaru/next.js,flybayer/next.js,azukaru/next.js,JeromeFitz/next.js,azukaru/next.js,zeit/next.js,flybayer/next.js,JeromeFitz/next.js