Update src/note_encryption.rs

Co-authored-by: str4d <jack@electriccoin.co>

src/note_encryption.rs

@@ -85,6 +85,7 @@ pub struct OrchardDomain {
 }
 
 impl OrchardDomain {
+    /// Constructs a domain that can be used to trial-decrypt this action's output note.
     pub fn for_action<T>(act: &Action<T>) -> Self {
         OrchardDomain { rho: *act.nullifier() }
     }