Updated the documentation

README.md

@@ -5,4 +5,38 @@ A set of csv files processing utilities inspired by [csvkit](https://github.com/
 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.
+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.
+
+## Example
+
+```bash
+$ head wine.csv
+Wine,Alcohol,Malic.acid,Ash,Acl,Mg,Phenols,Flavanoids,Nonflavanoid.phenols,Proanth,Color.int,Hue,OD,Proline
+1,14.23,1.71,2.43,15.6,127,2.8,3.06,.28,2.29,5.64,1.04,3.92,1065
+1,13.2,1.78,2.14,11.2,100,2.65,2.76,.26,1.28,4.38,1.05,3.4,1050
+1,13.16,2.36,2.67,18.6,101,2.8,3.24,.3,2.81,5.68,1.03,3.17,1185
+1,14.37,1.95,2.5,16.8,113,3.85,3.49,.24,2.18,7.8,.86,3.45,1480
+1,13.24,2.59,2.87,21,118,2.8,2.69,.39,1.82,4.32,1.04,2.93,735
+1,14.2,1.76,2.45,15.2,112,3.27,3.39,.34,1.97,6.75,1.05,2.85,1450
+1,14.39,1.87,2.45,14.6,96,2.5,2.52,.3,1.98,5.25,1.02,3.58,1290
+1,14.06,2.15,2.61,17.6,121,2.6,2.51,.31,1.25,5.05,1.06,3.58,1295
+1,14.83,1.64,2.17,14,97,2.8,2.98,.29,1.98,5.2,1.08,2.85,1045
+
+$ cat wine.csv  | ./target/release/csvgr sql "select Wine, avg(Alcohol) from this group by Wine" | ./target/release/csvgr print
+shape: (3, 2)
+┌──────┬───────────┐
+│ Wine ┆ Alcohol   │
+│ ---  ┆ ---       │
+│ i64  ┆ f64       │
+╞══════╪═══════════╡
+│ 3    ┆ 13.15375  │
+├╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌┤
+│ 1    ┆ 13.744746 │
+├╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌┤
+│ 2    ┆ 12.278732 │
+└──────┴───────────┘
+```
+
+## Built standing on the shoulders of giants
+
+None of this would be possible without [Polars](https://github.com/pola-rs/polars)