Add robots.txt, modify front matter

website/docs/cmixx/adrp.md

website/docs/cmixx/cmixx.md

website/docs/cmixx/coverTraffic.md

website/docs/cmixx/design-specs/architecture.md

website/docs/cmixx/design-specs/cmixx.md

website/docs/cmixx/design-specs/dm.md

website/docs/cmixx/design-specs/end_to_end.md

website/docs/cmixx/design-specs/gateway_gossip.md

website/docs/cmixx/design-specs/gateway_mixing.md

website/docs/cmixx/design-specs/message_pickup.md

website/docs/cmixx/design-specs/multicast_channel.md

website/docs/cmixx/design-specs/pki.md

website/docs/cmixx/design-specs/threat_model.md

website/docs/cmixx/design-specs/wire.md

website/docs/cmixx/e2e-xxm.md

website/docs/cmixx/idCollisionAndNotifications.md

website/docs/cmixx/userDiscovery.md

website/docs/cmixx/xxdk/getting-started.md

website/docs/cmixx/xxdk/guides/cmix-client-keystore.md

website/docs/cmixx/xxdk/guides/ndf-retrieval.md