Mobile landing page in Capella dev docs

https://docs.couchbase.com/cloud/mobile-guides/intro.html

https://github.com/couchbaselabs/docs-devex/blob/capella/modules/mobile-guides/pages/intro.adoc

This page needs to be more informative and useful for mobile developers:

1. Link to CBL, not the Mobile landing page (which talks about SGW)
2. Intro text about mobile development
3. Look as a quickstart on mobile dev with Capella (create endpoints, get connection string, head off to CBL pages?)