Clarify key properties in docs

Co-authored-by: Angus Hollands <[email protected]>

Author: GeorgianaElena

docs/source/jupyterhub/customizing/user-resources.md

@@ -118,12 +118,14 @@ The following configuration will increase the SHM allocation by mounting a
 singleuser:
   storage:
     extraVolumes:
-      shm-volume:
+      # Arbitrary key for identity & ordering
+      1-shm-volume:
         name: shm-volume
         emptyDir:
           medium: Memory
     extraVolumeMounts:
-      shm-volume:
+      # Arbitrary key for identity & ordering
+      1-shm-volume:
         name: shm-volume
         mountPath: /dev/shm
 ```

docs/source/jupyterhub/customizing/user-storage.md

@@ -235,12 +235,14 @@ pods:
 singleuser:
   storage:
     extraVolumes:
-      jupyterhub-shared:
+      # Arbitrary key for identity & ordering
+      1-jupyterhub-shared:
         name: jupyterhub-shared
         persistentVolumeClaim:
           claimName: jupyterhub-shared-volume
     extraVolumeMounts:
-      jupyterhub-shared:
+      # Arbitrary key for identity & ordering
+      1-jupyterhub-shared:
         name: jupyterhub-shared
         mountPath: /home/shared
 ```