Share roadmap in documentation

[daanpape]

Based on community feedback it would be a good idea to share our roadmap in the docs. The current roadmap is:

1. Documentation upgrades
2. We are working on a 'Unified Communications' library. That's a more high level library than WalterModem that's based on esp-modem and actually uses the PPP function of the modem. It will allow for seamless switching between WiFi, Ethernet and cellular.
3. Extended examples (like AWS, and Azure integration)