explain use of SetParamsGate for updating pwc pulse

Author: lazyoracle

examples/Piecewise_constant_controls.ipynb

@@ -550,6 +550,20 @@
     "plot_dynamics(simulation, model.get_init_state(), [\"rx90p[0]\"])"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Updating the piecewise pulse description in qiskit"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "We now use the `SetParamsGate` to update the pwc pulse description for the previously built qiskit circuit. This `SetParamsGate` must always be added only once and only at the end of the circuit. It can be used for updating the description of as many `Instructions` (and more generally as many c3 experiment `Parameter`s) as desired through a single instance of the gate. The updated parameter values is the first element and the paramater_map for this update is the second element in the list being passed to the `params` argument of the `SetParamsGate` below. "
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": 20,
@@ -621,7 +635,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.9.7"
+   "version": "3.8.12"
   }
  },
  "nbformat": 4,