Update MCP docs

[digitarald]

Based on latest updates and feedback:

• Support matrix (tools, roots)
• Latest setup tips (envFile)
• Getting started on creating a server and tips for tool developers (description)
• How to create install/button instructions for server devs

[digitarald]

fyi, @connor4312 anything I missed that cames up more frequently in feedback? Otherwise I start wordsmithing

[connor4312]

Sounds like a good start, let's get something drafted and we can iterate :)

[ntrogh]

@digitarald MCP docs are invnext branch. Give me another 15 minutes to merge my latest updates. Restructuring much of the Copilot docs due to unified chat view.

[digitarald]

@ntrogh took a first stab here: 8b947b5

[ntrogh]

@digitarald LGTM. Thanks!