API SDK documentation for JS, Android, and iOS

The docs are hosted on https://developer.nexmo.com/client-sdk/overview

Making changes

• After updating the docs in this repo, navigate to your local copy of nexmo-developer
• Run the rake task $ rake repos:pull nexmo/conversation-docs
• Make a PR with your changes to the nexmo-developer repo
• Merge the PR and deploy a new version of the nexmo-developer site