spec_25: clarify that or-slots and xor-slots are not supported

Add a note to RFC 25 (Job Specification Version 1) clarifying that
V1 jobspec does not support alternative slot configurations including
or-slots (sibling slot resources) and xor_slot resource types.

These advanced features require the flexible traverser and are only
available in the canonical jobspec format (RFC 14).

This clarification helps users understand the limitations of V1 jobspec
and directs them to RFC 14 when they need alternative slot functionality.

Assisted-by: Claude <noreply@anthropic.com>

Author: Zeke Chadron Blair Morton

spec_25.rst

@@ -127,6 +127,14 @@ well. Therefore, the complete enumeration of valid resource graphs in V1 is:
 
 -  ``node>slot>(core,gpu)``
 
+Alternative Slot Configurations
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Version 1 jobspec does NOT support alternative slot configurations such as
+or-slots (sibling ``slot`` resources) or ``xor_slot`` resource types. These
+advanced features require the flexible traverser and are only available in the
+canonical jobspec format described in :doc:`RFC 14 <spec_14>`.
+
 Tasks
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