docs: add optional Parallel Search MCP example

[georgeatparallel]

Summary

• add an optional named Parallel Search entry to the existing mcpServers configuration example
• set transportType to streamable-http explicitly because URL-only remote entries otherwise use SSE
• disclose that selected search queries and requested URLs are sent to Parallel.ai

No authentication, headers, credentials, defaults, existing providers, or runtime behavior are changed.

Validation

• verified the exact entry, endpoint, transport, disclosure, and placement between the existing Amap and Notion examples
• git diff --check
• git status --short (only docs/CONFIGURATION.md is modified)

Disclosure: I work at Parallel.ai, which operates this MCP endpoint.