doc: update overview with new API

Mention the new Progress and TurnByTurn APIs.

Apertis: https://phabricator.apertis.org/T2816



Signed-off-by: Guillaume Desmottes <guillaume.desmottes@collabora.co.uk>
Reviewed-by: Justin Kim <justin.kim@collabora.com>
Differential Revision: https://phabricator.apertis.org/D5381

docs/reference/markdown_files/traprain-overview.markdown

@@ -21,6 +21,15 @@ Once initialized, it will take care to claim the
 They should then use its API to publish potential navigation routes,
 represented as [TrpRoute](traprain-common/route.h) objects.
 
+They can also create a [TrpServiceNavigationGuidanceProgress](traprain-service/navigation-guidance-progress.h)
+object to publish information about the current journey, such as its start and estimated end time.
+Once initialized, it will take care to claim the
+`org.apertis.NavigationGuidance1.Progress` D-Bus well-known name and expose the
+`/org/apertis/NavigationGuidance1/Progress` object on the bus.
+
+System services can use the [TrpServiceTurnByTurnNotification](traprain-service/turn-by-turn-notification.h)
+API to send turn-by-turn notifications to the UI responsible of displaying them.
+
 ### Client side API
 
 SDK applications willing to retrieve the routing information shared by the
@@ -31,6 +40,24 @@ which will take care of communicating with the navigation service using D-Bus.
 Each potential navigation route will be exposed by this object using
 [TrpClientRoute](TrpClientRoute) objects.
 
+In order to retrieve information about the current journey, they should create and initialize a
+[TrpClientNavigationGuidanceProgress](traprain-client/navigation-guidance-progress.h) object
+which will take care of communicating with the navigation service using D-Bus.
+
+### Guidance API
+
+The UI responsible of displaying turn-by-turn notifications has to use the
+*traprain-guidance* library.
+
+They should create and initialize a [TrpGuidanceTurnByTurnService](traprain-guidance/turn-by-turn-notification.h) object
+which will take care of communicating with the navigation service using D-Bus.
+Once initialized, it will take care to claim the
+`org.apertis.NavigationGuidance1.TurnByTurn` D-Bus well-known name and expose the
+`/org/apertis/NavigationGuidance1/TurnByTurn` object on the bus.
+
+Notifications received for displaying from the navigation system will be represented as
+[TrpGuidanceTurnByTurnNotification](traprain-guidance/turn-by-turn-notification.h) objects.
+
 ### Mock service
 
 In order to allow developers to test their code using the SDK emulator,