README.md: rework the JSON schema section

Signed-off-by: Nicolas Buffon <nicolas.buffon@orange.com>

README.md

@@ -57,12 +57,26 @@ Sent traces include the following parameters:
     - `iot3.core.mqtt.payload_size` 
     - `iot3.core.sdk_language`
 
-Packages
---------
 
-### JSON Schema
+JSON schemas
+------------
+
+_**WIP ...**_
+
+[ETSI.org][3] proposal of implementation using the [JSON][2] language (instead of ASN.1 UPER by default) of the following messages:
+- CooperativeAwarenessMessage (CAM)
+- CollectivePerceptionMessage (CPM)
+- DecentralizedEmergencyNotificationMessage (DENM)
+
+Custom messages for V2X:
+- Information
+- Status
+
+_Note: none of the provided implementation is able to use different version of a schema, they are then using the most
+recent one_
 
-[ETSI.org][3] proposal of implementation using the [JSON][2] language (instead of ASN.1 UPER by default).
+Languages
+---------
 
 ### Rust