Add example of sending from ext context

Author: jazzz

src/nim_chat_poc.nim

@@ -1,6 +1,7 @@
 import
   chronicles,
-  chronos
+  chronos,
+  strformat
 
 import
   waku_client
@@ -10,11 +11,19 @@ proc handleMessages(pubsubTopic: string, message: seq[byte]): Future[
     void] {.gcsafe, raises: [Defect].} =
   info "ClientRecv", pubTopic = pubsubTopic, msg = message
 
+proc demoSendLoop(client: WakuClient): Future[void] {.async.} =
+  for i in 1..10:
+    await sleepAsync(20.seconds)
+    discard client.sendMessage(&"Message:{i}")
+
 proc main(): Future[void] {.async.} =
   echo "Starting POC"
   let cfg = DefaultConfig()
   let client = initWakuClient(cfg, @[PayloadHandler(handleMessages)])
-  await client.start()
+  asyncSpawn client.start()
+
+  await demoSendLoop(client)
+
   echo "End of POC"
 
 when isMainModule: