Getting the assets (For Mappers)

Simply download the ZIP:

Then open it and go into the surf_minigolf-master folder for the folders you want to extract and drag-and-drop these folders into your game directory:

Source Engine Folders for contributing (For Artists)

maps
mapsrc
models/surf_minigolf
materials

Are all there to mirror Source's folder structure, so place game assets into them.
Any other folders are for source files that the game doesn't use.

Symlinks (For Mappers/Artists using Git or some other directory who don't like copying everything every time)

DISCLAIMER: I only figured out about this the other day, but it is so useful that I had to include it here.
I am not an expert on this, so ask someone else if my writing doesn't explain it well enough :V

If you're using Git to fetch/pull this repo for updates, you might want to use symlinks so updates are reflected inside your game's directory so there is no need to copy files over each time.

You can use the regular CMD mklink method or for much more convenience use Link Shell Extension, which i'll show below.

On the page, click Download in the Quick Start section to avoid a minute of scrolling. This is the link you'll want:

Download it, scan it if you want (good habit imo) and then install it.
It will mention closing Explorer and attempting to restart it; let it do that unless you want to restart I suppose :v

At some point you'll have it installed and will now have this option in the Right-Click menu for files and folders:

Which is what you will use to designate what you want to be "mirrored" elsewhere.

So you can right click a sub-folder as the Link Source...

Important Note about folders really quick:

The folder/file must not exist already, so that's why you want to go into a sub-folder; go through until you reach a folder which your game directory doesn't have.

In this above example, I can copy surf_minigolf as a symlink because it doesn't exist in my momentum/materials folder, but not the models folder above it, because it does exist.

...then right click in your game's matching folder and use the new Drop As... > option:

This menu has several options that i've never heard of before. Nobody actually knows what a "Delorean Copy" is.
JUST SELECT SYMBOLIC LINK. It's what i've been using.

Then you should have a slightly different looking folder appear:

Your shortcut icon may appear with a green arrow instead, this is normal and part of the install.

It's a shortcut... but it's a folder...