Add a search piped to jq example to the docs

[bhekanik]

Add one or two practical examples showing mxr search ... --format json | jq ... in the README or docs site.

Acceptance criteria:

• Add at least one copy-pastable mxr search + jq example
• Keep the example agent/shell-friendly, not TUI-only
• Put it in the most discoverable doc location for new users
• Verify the command syntax matches the current CLI