[Proposal] Add Microsoft Learn MCP Server

I would have assumed that a skill referencing the [Microsoft Learn MCP Server](https://learn.microsoft.com/en-us/training/support/mcp-get-started) would be included, since it's essential for agents to get documentation on dotnet APIs.

I realize an MCP server isn't the same as a skill and that Microsoft Learn isn't dotnet-specific, but it seems important enough that an agent could still be made aware of it so it can install it or at least tell the user.

If not, maybe mention it in the README so users/agents can be aware that it exists?

Start by reviewing the existing skills and README, then read the linked Microsoft Learn MCP Server documentation to understand how it should be presented. Decide whether the server belongs as a skill or a README reference, and consider the work done when users and agents can discover the server and understand how to install or use it.

Written by the indexing model from the issue text.