Added What is Offline First? video
Added What is Offline First? video

Replaced network bar graphic with our new What is Offline First? video
ibm-watson-data-lab/ibm-watson-data-lab.github.io,ibm-watson-data-lab/ibm-watson-data-lab.github.io,ibm-watson-data-lab/ibm-watson-data-lab.github.io,ibm-watson-data-lab/ibm-watson-data-lab.github.io