Update installation command in Rigetti demo notebook

Author: pavoljuhas

docs/hardware/rigetti/getting_started.ipynb

@@ -109,11 +109,13 @@
    "source": [
     "try:\n",
     "    import cirq\n",
+    "    import cirq_rigetti\n",
     "except ImportError:\n",
-    "    print(\"installing cirq...\")\n",
-    "    !pip install --quiet cirq\n",
-    "    print(\"installed cirq.\")\n",
-    "    import cirq"
+    "    print(\"installing cirq-rigetti...\")\n",
+    "    !pip install --quiet cirq-rigetti\n",
+    "    print(\"installed cirq-rigetti.\")\n",
+    "    import cirq\n",
+    "    import cirq_rigetti"
    ]
   },
   {