[Feature] Instruct how to install `uvx` for MCP skill

[dbeatty10]

Problem

The uvx CLI is a prerequisite of the MCP skill. But it is not explicitly stated that way. Nor does it include instructions for resolving that scenario if it is not installed.

Proposed solution

• Include uvx as a prerequisite
• Share how to check if it is installed or not
• Provide instructions how to install it for various platforms