Add procedure for computing root from proof

tips/TIP-0045/tip-0045.md

@@ -215,7 +215,14 @@ A **merkle proof** is computed as follows:
 
 ### Root Computation
 
-The **merkle root** is the result of `Hash Subtree(Leaves)`.
+The **merkle root** can be computed from two different inputs:
+
+- From an array of `Leaves` by calling `Hash Subtree(Leaves)`.
+- From a merkle proof by calling `Hash Component` the top-level component of the proof, where `Hash Component` is
+  defined as:
+  - If the component is a `Leaf Hash`, return its field `Hash`.
+  - If the component is a `Value Hash`, return its field `Hash`.
+  - If the component is a `Node` return `Hash Node(Hash Component(Left), Hash Component(Right))`.
 
 # Detailed design