Add note about setting fractional gates flag

docs/guides/get-started-with-primitives.ipynb

@@ -11,6 +11,16 @@
     "\n",
     "<Admonition type=\"note\">\n",
     "    While this documentation uses the primitives from Qiskit Runtime, which allow you to use IBM&reg; backends, the primitives can be run on any provider by using the [backend primitives](#backend) instead.  Additionally, you can use the *reference* primitives to run on a local statevector simulator.  See [Exact simulation with Qiskit primitives](simulate-with-qiskit-sdk-primitives) for details.\n",
+    "</Admonition>\n",
+    "\n",
+    "<Admonition type=\"note\" title=\"Using Fractional Gates\">\n",
+    "    If you wish to use the newly supported [fractional gates](./fractional-gates), you will need to set `use_fractional_gates=True` when requesting a backend from a `QiskitRuntimeService` instance. For example:\n",
+    "    ``` python\n",
+    "    service = QiskitRuntimeService()\n",
+    "    fractional_gate_backend = service.least_busy(use_fractional_gates=True)\n",
+    "    ```\n",
+    "\n",
+    "    However, note that this is an experimental feature and may change in the future.\n",
     "</Admonition>"
    ]
   },