Add manual client configuration examples

[SrFlipFlop]

Why

The current README mostly documents Claude Desktop plus generic manual installation notes. In practice, users are also trying to connect Burp MCP to other agent clients, but the exact working configuration differs depending on whether the client supports SSE directly or needs a stdio proxy.

This change adds concrete, copy-pasteable examples for clients that were tested and confirmed working, so users do not need to infer the correct configuration from the Claude-specific instructions.

Scope

This PR is documentation-only:

• no runtime changes
• no extension UI changes
• no new installer integrations

I intentionally left out unverified client examples to keep the guidance accurate and minimal.

Related issues

• Helps with #46 by adding concrete MCP client configuration examples.
• Related to #38, which asks for clearer non-Claude-Desktop setup guidance.
• May help users hitting #42 by clarifying direct SSE endpoint options.

Notes

• OpenCode and GitHub Copilot CLI can connect directly to the Burp SSE endpoint.
• Codex CLI works well through the packaged stdio proxy.
• Depending on the client, the Burp endpoint may need to be configured as either:
  • http://127.0.0.1:9876
  • http://127.0.0.1:9876/sse

Manual verification

• verified OpenCode against a local Burp MCP server
• verified GitHub Copilot CLI against a local Burp MCP server
• verified Codex CLI against a local Burp MCP server via mcp-proxy-all.jar