resolveSymBV: Make note of possible future work

See also #188

what4/src/What4/Utils/ResolveBounds/BV.hs

@@ -70,6 +70,14 @@ data SearchStrategy
     --   bounds of the search and 'BV.maxUnsigned' as the rightmost bounds of
     --   the search.
 
+  -- Some possibilities for additional search strategies include:
+  --
+  -- - Using Z3's minimize/maximize commands. See
+  --   https://github.com/GaloisInc/what4/issues/188
+  --
+  -- - A custom, user-specified strategy that uses callback(s) to guide the
+  --   search at each iteration.
+
 -- | Use an 'WPO.OnlineSolver' to attempt to resolve a 'WI.SymBV' as concrete.
 -- If it cannot, return the lower and upper bounds. This is primarly intended
 -- for compound expressions whose bounds cannot trivially be determined by