doc: add overview & license section in readme.md

README.md

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     <h1>PRQLite</h1>
     <p>Use SQLite database with <a href="https://github.com/prql/prql">PRQL</a></p>
 </div>
+
+# Overview
+PRQL is a modern language for transforming data. It's simple and really powerful. You can do a lot with a few simple lines. But with Prqlite, You can use it with SQLite database along with a lot of features.
+[![asciicast](https://asciinema.org/a/604334.svg)](https://asciinema.org/a/604334)
+
+# License
+Prqlite is available under the [GPL-2](https://www.gnu.org/licenses/old-licenses/gpl-2.0.en.html) license.
+For more, you can read the [License](LICENSE) file.
+
+<div align="center">
+
+[![GitHub license](https://img.shields.io/github/license/Hulxv/vnstat-server?style=for-the-badge)](LICENSE)
+
+</div>