Add lines of code badge to README (#125)

Author: nietras

README.md

@@ -1,6 +1,7 @@
 # Sep - ~~Possibly~~ the World's Fastest .NET CSV Parser
 ![.NET](https://img.shields.io/badge/net7.0%20net8.0-5C2D91?logo=.NET&labelColor=gray)
 ![C#](https://img.shields.io/badge/12.0-239120?logo=csharp&logoColor=white&labelColor=gray)
+![Lines of code](https://tokei.rs/b1/github/nietras/Sep?category=code)
 [![Build Status](https://github.com/nietras/Sep/actions/workflows/dotnet.yml/badge.svg?branch=main)](https://github.com/nietras/Sep/actions/workflows/dotnet.yml)
 [![Super-Linter](https://github.com/nietras/Sep/actions/workflows/super-linter.yml/badge.svg)](https://github.com/marketplace/actions/super-linter)
 [![codecov](https://codecov.io/gh/nietras/Sep/branch/main/graph/badge.svg?token=WN56CR3X0D)](https://codecov.io/gh/nietras/Sep)