docs(readme): reorganize for readability, add long-running, Hermes and multi-agent sections

Install routes, the collapsible platform, language and FAQ sections and
the new feature sections come first; benchmarks, the repository layout,
releases, community and documentation form the reference half at the
bottom. Nothing removed, only moved. New sections: "Built for
long-running agent tasks" (what breaks long runs and which shipped
mechanism answers it), "Hermes Agent: first-class support (CLI and
Desktop)" and "Multi-agent runs: orchestrators, workers and subagents",
each grounded in mechanisms that already ship. Hermes rows in the tier
and command tables, the v3.13.0 releases row, and the Hermes install
route in Quick Install.