Post spawn docs (#95)

docs/signals.rst

@@ -13,6 +13,12 @@ Before enqueuing a task
 The ``django_q.signals.pre_enqueue`` signal is emitted before a task is
 enqueued. The task dictionary is given as the ``task`` argument.
 
+After spawning a worker process
+"""""""""""""""""""""""""""""""
+
+The ``django_q.signals.post_spawn`` signal is emitted after a worker process has
+spawned. The process name is given as the ``proc_name`` argument (string).
+
 Before executing a task
 """""""""""""""""""""""
 
@@ -37,7 +43,7 @@ Connecting to a Django Q2 signal is done the same as any other Django
 signal::
 
     from django.dispatch import receiver
-    from django_q.signals import pre_enqueue, pre_execute, post_execute
+    from django_q.signals import pre_enqueue, pre_execute, post_execute, post_spawn
 
     @receiver(pre_enqueue)
     def my_pre_enqueue_callback(sender, task, **kwargs):
@@ -51,4 +57,8 @@ signal::
     def my_post_execute_callback(sender, task, **kwargs):
         print(f"Task {task['name']} was executed with result {task['result']}")
 
+    @receiver(post_spawn)
+    def my_post_spawn_callback(sender, proc_name, **kwargs):
+        print(f"Process {proc_name} has spawned")
+