Automate carbon image creation

[Maxime Mouchet]

We use carbon.now.sh to create the image in the README.
Can we automate this process ?

The image should contains the following text (or similar):

$ sncf-cli search Lyon Paris
[sncf-cli output, truncated to first proposal]
...

The configuration file from carbon.now.sh is:

{
  "paddingVertical": "45px",
  "paddingHorizontal": "38px",
  "marginVertical": "45px",
  "marginHorizontal": "45px",
  "backgroundImage": null,
  "backgroundImageSelection": null,
  "backgroundMode": "color",
  "backgroundColor": "rgba(239,40,44,0)",
  "dropShadow": true,
  "dropShadowOffsetY": "20px",
  "dropShadowBlurRadius": "27px",
  "theme": "material",
  "windowTheme": "none",
  "language": "text",
  "fontFamily": "Hack",
  "fontSize": "14px",
  "lineHeight": "143%",
  "windowControls": true,
  "widthAdjustment": false,
  "lineNumbers": false,
  "exportSize": "4x",
  "watermark": false,
  "squaredImage": false,
  "loading": false,
  "aspectRatio": 2.1377551020408165,
  "icon": "/static/presets/1.png",
  "isVisible": true
}

[Maxime Mouchet]

Not really needed.