Save the file to your /mods folder. And remove the .txt extension after downloading it from your browser, the filename should only be user.lua

Features:

• Shows bag usage in the lobby
• Custom stats line
• Type /ammo in chat to show how much ammo you have in your loadout
• Type /reload to reload your mod overrides
• Show player gameplay altering mods
• Toggle sight upgrades with "num 4"
• "num 1" to re-register lobby - this is useful if you have lost connection to Steam and no one seems to be joining your lobby
• Show player stats at endscreen
• Much more...

Remember, everything is configurable and you can make your own tweaks.