Add 'Verify cooling fans' section

[wridgers]

Verifying the cooling fans are correctly wired up is an essential step that, if missed, can lead to difficult to diagnose clogging and part quality problems.

[netlify[bot]]

✅ Deploy Preview for dev-voron-documentation ready!

Name	Link
🔨 Latest commit	679ee87d882c007f6c5a0c30743bd2ee66d3ce90
🔍 Latest deploy log	https://app.netlify.com/sites/dev-voron-documentation/deploys/6614701c85a4c00008b21118
😎 Deploy Preview	https://deploy-preview-414--dev-voron-documentation.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[maz0r]

@wridgers The heatsink cooling fan should be spinning all the time.

Should probably read The heatsink cooling fan should be spinning whenever the hotend is active or above 50C as that's the default behaviour :)