Update How_to_count_tokens_with_tiktoken.ipynb (openai#368)

* Update How_to_count_tokens_with_tiktoken.ipynb

add c# tiktoken lib.

* Update How_to_count_tokens_with_tiktoken.ipynb

fix format.

* Update How_to_count_tokens_with_tiktoken.ipynb

fix format.

Author: aiqinxuancai

examples/How_to_count_tokens_with_tiktoken.ipynb

@@ -1,6 +1,7 @@
 {
  "cells": [
   {
+   "attachments": {},
    "cell_type": "markdown",
    "metadata": {},
    "source": [
@@ -36,7 +37,7 @@
     "\n",
     "For `cl100k_base` and `p50k_base` encodings:\n",
     "- Python: [tiktoken](https://github.com/openai/tiktoken/blob/main/README.md)\n",
-    "- .NET / C#: [SharpToken](https://github.com/dmitry-brazhenko/SharpToken)\n",
+    "- .NET / C#: [SharpToken](https://github.com/dmitry-brazhenko/SharpToken), [TiktokenSharp](https://github.com/aiqinxuancai/TiktokenSharp)\n",
     "- Java: [jtokkit](https://github.com/knuddelsgmbh/jtokkit)\n",
     "\n",
     "For `r50k_base` (`gpt2`) encodings, tokenizers are available in many languages.\n",