Add rationale

README.md

@@ -1,3 +1,8 @@
 # csvgr.rs
 
-A set of csv files processing utilities inspired by [csvkit](https://github.com/wireservice/csvkit) with blazing speed, powered by Rust.
+A set of csv files processing utilities inspired by [csvkit](https://github.com/wireservice/csvkit) with blazing speed, powered by Rust.
+
+You may wonder why I'm implementing this, since there's already [xsv](https://github.com/BurntSushi/xsv). There are two reasons for that:
+
+1. This is the project I'm implementing to learn Rust
+2. The Rust data ecosystem has evolved immensely since xsv was sarted. Now we can add things like SQL commands to filter csv files, or translate results to parquet files.