[Doc] add introduction

README.md

@@ -1,6 +1,14 @@
 <img width="350" src="/doc/logo.png" />
 
 ## CodeSnap
+CodeSnap is a pure Rust tool for generate beautiful code snapshots, it directly use graphic engine to generate snapshots, which means the entire process is just matter of computation and rendering, without need for network or something like browser-based rendering solution.
+
+Generally, you can directly use CLI tool provide by CodeSnap to generate code snapshots you want. Or CodeSnap also provide a library for you to integrate it into your own project, so you can generate code snapshots in your own way (See [Related projects](#) for more information).
+
+## Related projects
+- [codesnap-cli]()
+- [codesnap.nvim]()
+
 
 ## License
 MIT.