Github can be confusing to navigate. Parts of it still baffle me too.

Start from the page for the pull request:
johnrickman/LiquidCrystal_I2C#16

@Pigeo gives a link to a commit:
johnrickman/LiquidCrystal_I2C@079b4f8

On the right of the page, fairly near the top, you'll see a button labelled "Browse files". That takes you to:
https://github.com/johnrickman/LiquidCrystal_I2C/tree/079b4f81228490d8692497b5ed363dcea7ec43e7

There you will see a button labelled "Code", to the right of the middle (depending on zoom level etc), fairly near the top. Click that then click "Download ZIP", at the bottom of the box that appears. That gets you the main .h and .cpp plus a folder of example sketches to use them with.