Add Merkle Tree to the docs

contracts/utils/README.adoc

@@ -21,6 +21,7 @@ Miscellaneous contracts and libraries containing utility functions you can use t
  * {EnumerableSet}: Like {EnumerableMap}, but for https://en.wikipedia.org/wiki/Set_(abstract_data_type)[sets]. Can be used to store privileged accounts, issued IDs, etc.
  * {DoubleEndedQueue}: An implementation of a https://en.wikipedia.org/wiki/Double-ended_queue[double ended queue] whose values can be removed added or remove from both sides. Useful for FIFO and LIFO structures.
  * {Checkpoints}: A data structure to store values mapped to an strictly increasing key. Can be used for storing and accessing values over time.
+ * {MerkleTree}: A library with https://wikipedia.org/wiki/Merkle_Tree[Merkle Tree] data structures and helper functions.
  * {Create2}: Wrapper around the https://blog.openzeppelin.com/getting-the-most-out-of-create2/[`CREATE2` EVM opcode] for safe use without having to deal with low-level assembly.
  * {Address}: Collection of functions for overloading Solidity's https://docs.soliditylang.org/en/latest/types.html#address[`address`] type.
  * {Arrays}: Collection of functions that operate on https://docs.soliditylang.org/en/latest/types.html#arrays[`arrays`].
@@ -91,6 +92,8 @@ Ethereum contracts have no native concept of an interface, so applications must
 
 {{Checkpoints}}
 
+{{MerkleTree}}
+
 == Libraries
 
 {{Create2}}