Update week4.do.txt

Author: mhjensen

doc/src/week4/week4.do.txt

@@ -637,6 +637,8 @@ Using this result, we obtain
 
 The whiteboard notes for this week contain other examples of one qubit gates and their relation to specific unitary transformations and effective Hamiltonian, see URL:"https://github.com/CompPhysics/QuantumComputingMachineLearning/blob/gh-pages/doc/HandWrittenNotes/2025/NotesFebruary12.pdf"
 
+# material to be added
+
 !split
 ===== Part 3: Famous Quantum gates, circuits and simple algorithms (repetition  from last week) =====