events: Restore docs for DummyEvent and RoomKeyEvent

crates/ruma-events/src/dummy.rs

@@ -4,6 +4,16 @@ use ruma_events_macros::EventContent;
 use serde::{Deserialize, Serialize};
 
 /// The payload for `DummyEvent`.
+///
+/// This event type is used to indicate new Olm sessions for end-to-end encryption.
+///
+/// Typically it is encrypted as an *m.room.encrypted* event, then sent as a to-device event.
+///
+/// The event does not have any content associated with it. The sending client is expected to
+/// send a key share request shortly after this message, causing the receiving client to process
+/// this *m.dummy* event as the most recent event and using the keyshare request to set up the
+/// session. The keyshare request and *m.dummy* combination should result in the original
+/// sending client receiving keys over the newly established session.
 #[derive(Clone, Debug, Deserialize, Serialize, EventContent)]
 #[ruma_event(type = "m.dummy")]
 pub struct DummyToDeviceEventContent {}

crates/ruma-events/src/room_key.rs

@@ -5,6 +5,8 @@ use ruma_identifiers::{EventEncryptionAlgorithm, RoomId};
 use serde::{Deserialize, Serialize};
 
 /// The payload for `RoomKeyEvent`.
+///
+/// Typically encrypted as an *m.room.encrypted* event, then sent as a to-device event.
 #[derive(Clone, Debug, Deserialize, Serialize, EventContent)]
 #[ruma_event(type = "m.room_key")]
 pub struct RoomKeyToDeviceEventContent {