README.md: add advantages

No dependencies. 72kb file size. Less than 6kb gzipped file size!

Author: ramiy

README.md

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 Visualization help end-users understand data. **Charts.css** help frontend developers turn data into beautiful charts and graphs using simple **CSS classes**.
 
+No dependencies. 72kb file size. Less than 6kb gzipped file size!
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 ## Documentation
 
 Check the full documentation on [ChartsCSS.org](https://ChartsCSS.org/).