readme fix (#26)

Author: dmitry-brazhenko

README.md

@@ -11,7 +11,7 @@
 
 
 SharpToken is a C# library that serves as a port of the Python [tiktoken](https://github.com/openai/tiktoken) library.
-It provides functionality for encoding and decoding tokens using GPT-based encodings. This library is built for .NET 6
+It provides functionality for encoding and decoding tokens using GPT-based encodings. This library is built for .NET 6, .NET 8
 and .NET Standard 2.0, making it compatible with a wide range of frameworks.
 
 ## Installation