Add missing m.call descriptions

event-schemas/schema/v1/m.call.answer

@@ -14,7 +14,7 @@
                 },
                 "answer": {
                     "type": "object",
-                    "description": "",
+                    "description": "The session description object",
                     "properties": {
                         "type": {
                             "type": "string",

event-schemas/schema/v1/m.call.candidates

@@ -1,6 +1,7 @@
 {
     "$schema": "http://json-schema.org/draft-04/schema#",
     "type": "object",
+    "description": "This event is sent by callers after sending an invite and by the callee after answering. Its purpose is to give the other party additional ICE candidates to try using to communicate.",
     "allOf": [{
         "$ref": "core#/definitions/room_event"
     }],

event-schemas/schema/v1/m.call.invite

@@ -1,6 +1,7 @@
 {
     "$schema": "http://json-schema.org/draft-04/schema#",
     "type": "object",
+    "description": "This event is sent by the caller when they wish to establish a call.",
     "allOf": [{
         "$ref": "core#/definitions/room_event"
     }],