add docs about un-enqueueable reason

docs/design/podgroup-condition-reason.md

@@ -0,0 +1,25 @@
+# podgroup conditions
+
+## Backgrounds
+
+Currently, there are only two podgroup condition type: `Unschedulable` and `Scheduled`. If job is not enqueued, it has not been scheduled. And the event reason is `Unschedulable` and podgroup condition reason is `NotEnoughResources`. These reasons is not coresponding with the real reason `job is not enqueued`
+
+## Motivation
+
+In order to classify the uninqueueable reason from other unscheduleable reasons
+
+## Design
+
+1. add `Uninqueueable` reason for podgroup events
+
+```go
+ // PodGroupUnInqueueable is Uninqueueable event type
+ PodGroupUnInqueueable PodGroupConditionType = "Uninqueueable"
+```
+
+2. add `NotInqueueable` reason for podgroup conditions reason
+
+```go
+ // NotInqueueableReason if probed if job is rejected to enqueue
+ NotInqueueableReason string = "NotInqueueable"
+```