[YUNIKORN-810] constant KeyRequiredNode should be generated (#48)

diff --git a/scheduler-interface-spec.md b/scheduler-interface-spec.md
index dcb01da..8791ad6 100644
--- a/scheduler-interface-spec.md
+++ b/scheduler-interface-spec.md
@@ -675,6 +675,7 @@
 	// Keys
 	KeyPodName      = "podName"
 	KeyNamespace    = "namespace"
+	KeyRequiredNode = "requiredNode"
 )
 ```