Make sure to first have SuperBLT, and BeardLib installed. Click the links in the dependency list.

Optional video tutorial for installing SuperBLT, BeardLib, and mod_overrides mods: https://youtu.be/rin_sjSJIkg

1. After downloading the mod, use a program such as 7zip or WinRAR to extract the main folder of the mod.
2. Drop that folder into the mods folder which is supposed to be in the game's installation folder (don't know where that is? click here)

Developer Info:
For adding to existing weapons this template is a great example: https://modworkshop.net/mydownloads.php?action=view_down&did=24503

For adding to new attachments with XML:

<misc_attachment_stuff>
    <texture_variants>
        <template name_id="optional" desc_id="optional" texture_bundle_folder="optional" material_config="path"/>
    </texture_variants>
</misc_attachment_stuff>

Take a look at the template for specific details on values and examples of icon paths.