Update maintenance team duties according to latest discussions on dev call.

Signed-off-by: keenanjohnson <keenan.johnson@gmail.com>

- Link supported airframes to the Airframe reference rather than portfolio pages (they may look pretty, but nowhere near as useful for developers. Add portfolio link up top.
- Change the somewhat empty "Project Milestones" to "Project Roadmap" and link to the high level roadmap. I removed the only milestone about Lorenz creating the software. If we end up adding a more detailed milestone section that could go in. 
- Added clear guidelines for users vs developers.

Adding Sugnan Prabhu as maintainer for Intel Aero.
With great power comes great responsibility!

Refresh team list.

Added maintainers / corrected formatting.

With great power comes great responsibility!

Add GitHub links to maintenance team list.