Update FASM LUT metadata to clarify where it can be placed.

Signed-off-by: Keith Rothman <[email protected]>

Author: litghost

doc/src/utils/fasm.rst

@@ -148,6 +148,11 @@ example:
      </meta>
    </metadata>
 
+FASM LUT metadata must be attached to the ``<pb_type>`` at or directly above
+the ``<pb_type>`` with ``blif_model=".names"``.  The FASM LUT metadata tags
+will not be recognized attached inside of ``<mode>`` tags or inside
+``<pb_type>``'s higher than 1 level above the leaf type.
+
 When specifying a FASM features with more than one bit, explicitly specify the
 bit range being set.  This is required because "genfasm" does not have access
 to the actual bit database, and would otherwise not have the width of the