Link fix on start page. (quantumlib#5191)

Remove extra paranthesis.

Author: MichaelBroughton

docs/start.ipynb

@@ -112,7 +112,7 @@
    },
    "source": [
     "# Congratulations\n",
-    "You've just run your first Cirq program. If you would like to learn more about Quantum Computing, check out our [education page](/education). You can find more in depth tutorials [here](tutorials). The Full API reference for Cirq can be found [here]((/reference/python/cirq). If you are looking for vendor specific information that can be found on our vendor sub-pages:\n",
+    "You've just run your first Cirq program. If you would like to learn more about Quantum Computing, check out our [education page](/education). You can find more in depth tutorials [here](tutorials). The Full API reference for Cirq can be found [here](/reference/python/cirq). If you are looking for vendor specific information that can be found on our vendor sub-pages:\n",
     "\n",
     "\n",
     "  [Google Quantum Computing Service](tutorials/google/start.ipynb)\n",