Add documentation to TransitionMatrix comparison operator

src/include/TransitionMatrix.h

@@ -161,6 +161,17 @@ class TransitionMatrix {
    * (default is "LEGACY").
    */
   void write_binary(std::string file_name, std::string mode="LEGACY");
+  
+  /*! \brief Test whether two instances of TransitionMatrix are equal.
+   *
+   * Transition matrixes can be the result of a calculation or of a file input operation,
+   * reading from a previously computed object. The `==` operator tests for the equivalence
+   * of two transition matrixes, returning `true` if they are equivalnet, `false` otherwise.
+   *
+   * \param other: `TransitionMatrix &` Reference to the instance to be compared with.
+   * \return result: `bool` True, if the two instances are equal, false otherwise.
+   */
+  bool operator ==(TransitionMatrix &other);
 };
 
 #endif