This utility was made to simplify updating of directories that Tracker indexes. Tracker is the main way Gnome Shell searches for files (you might need to install Tracker first). Out of the box, it indexes only a couple of files in your $HOME. To make it useful the user needs to manipulate GSettings where Tracker stores it's configuration (by default).
To be able to use Gnome Shell file search in the overview you just need to install Tracker,
sudo apt install tracker
and then setup the directories you want it to track. This is where this script comes in.
To use it, create a configuration file named tracker-dirs and fill it with the directories you wish Tracker to index. Tracker has two modes - single for directories that are to be indexed non-recursively and recursive for (gasp) recursive indexing. Let the following example config file guide you:
[Recursive]
$HOME/foobar
[Single]
$HOME/foo/bar
$HOME/bar/bar
Then just run the script and log out. The overlay search should work the next time you log in.
It might take a while for Tracker to index your directories. You can view the indexing status using
tracker status