All Steam Guides are attached to a App ID or Game ID. For example if you search "Counter Strike: Global Offensive" on Steam you will find this page from the Steam Marketplace: https://gtm.you1.cn/app/730

As you can see in the URL the App ID for Counter Strike: Global Offensive is 730.

When you create a new guide Steam redirects you to a link which looks like this: http://gtm.you1.cn/sharedfiles/editguide/?appid=730

(This link, as you probably already noticed, will create a guide for Counter Strike, because appid=730).

If you change the App ID in the URL you can change the game which your guide will be attached, so you just need to use the Steam App ID (753).

You can use the following link to create a new guide to no specific game: http://gtm.you1.cn/sharedfiles/editguide/?appid=753