update README

Author: skanehira

README.md

@@ -1,9 +1,15 @@
 # code2img
-`code2img` can convert source code to image.
-This was inspired by [carbon](https://carbon.now.sh/) and [silicon](https://github.com/Aloxaf/silicon) but doesn't need browser & Internet.
+`code2img` can generate image of source code.
+This was inspired by [carbon](https://carbon.now.sh/) and [silicon](https://github.com/Aloxaf/silicon)
 
 ![](https://i.imgur.com/TjoOQct.gif)
 
+## Features
+-  Doesn't need browser & Internet
+-  Copy image of source code to clipboard
+-  Supported [some](https://github.com/alecthomas/chroma#supported-languages) color schemes
+-  Supported [some](https://xyproto.github.io/splash/docs/all.html) languages
+
 ## Usage
 ```sh
 $ code2img
@@ -22,6 +28,9 @@ Usage:
   -ext  file extension
 ```
 
+## Requirements
+- `xclip` (if copy image to clipboard in linux)
+
 ## Installtion
 
 ```sh