Add the localai-proxy known limits (no grammar or media forwarding,
TTS streams that end cleanly after an upstream failure, the /v1 path in
upstream_url), state that the Unimplemented skip covers the APIs that
answer HTTP 501, and describe a NATS-partitioned leader and pin
re-sync in distributed mode.
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>