chore: update soundness note on readme (#394)

* imp: update soundness note on readme

* Update README.md

---------

Co-authored-by: Aditya <[email protected]>

Author: colin-axner

README.md

@@ -70,6 +70,8 @@ Anyone interested in adding support for Solidity could pick up where [#58](https
 * [cometbft/crypto/merkle](https://github.com/cometbft/cometbft/tree/main/crypto/merkle)
 * [penumbra-zone/jmt](https://github.com/penumbra-zone/jmt)
 
+Supported merkle stores must be lexicographically ordered to maintain soundness. 
+
 ### Unsupported
 
 * [turbofish-org/merk](https://github.com/turbofish-org/merk)