Add missing operation name

Author: jean

index.ipynb

@@ -421,7 +421,7 @@
     "If you pass just `--help` after the operation name, you'll see a full list of all parameters accepted, and a link to the official GitHub documentation.\n",
     "\n",
     "```bash\n",
-    "ghapi --help\n",
+    "ghapi git.get_ref --help\n",
     ">>> git.get_ref(owner, repo, ref)\n",
     ">>> https://docs.github.com/rest/reference/git#get-a-reference\n",
     "```\n",