Official way of adding custom fonts to Rails 4?

Yes the link given will explain it well, however if u need another detailed explanation then here it is

• Firstly to use custom fonts in your app you need to download font files, you can try https://www.1001freefonts.com/ and look for fonts

  Few of the most popular font file formats are mainly .otf(Open Type Format) .ttf(True Type Format) .woff(Web Open Font Format)

• You can move the downloaded fonts to your app folder under app/assets/fonts/

• After downloading the file you need to “declare” the fonts you will be using in your css like this

  @font-face {
    font-family: "Kaushan Script Regular";
    src: url(/assets/KaushanScript-Regular.otf) format("truetype");
  }
  

• Finally you can use the font-family that you just declared wherever you want like this

  #e-registration {
    font-family: "Kaushan Script Regular";
  }
  

Hope this helps.