Fix: 10.2_Appendix_Tool Use - worng output

fixes: anthropics#23

prompt_engineering_interactive_tutorial/Anthropic 1P/10.2_Appendix_Tool Use.ipynb

@@ -118,7 +118,7 @@
    "source": [
     "system_prompt_tools_general_explanation = \"\"\"You have access to a set of functions you can use to answer the user's question. This includes access to a\n",
     "sandboxed computing environment. You do NOT currently have the ability to inspect files or interact with external\n",
-    "resources, except by invoking the below functions.\n",
+    "resources, except by invoking the below functions. Invoking a function is strictly optional.\n",
     "\n",
     "You can invoke one or more functions by writing a \"<function_calls>\" block like the following as part of your\n",
     "reply to the user:\n",