Document the preconditions for deleting a share

Document both the share status that allows deletion and
dependencies of the share that prevent share deletion.

Change-Id: I5f076112e66a2d50394639dce50390d8cfb4922b

api-ref/source/shares.inc

@@ -584,6 +584,16 @@ Delete share
 
 Deletes a share.
 
+Preconditions
+
+- Share status must be ``available``, ``error`` or ``inactive``
+
+- You cannot already have a snapshot of the share.
+
+- You cannot already have a group snapshot of the share.
+
+- You cannot already have a replica of the share.
+
 Response codes
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