Make an FAQ page

[emlys]

This came up in our discussion about the template for forum posts. In an FAQ page, we could expand on the points in the forum template and address other common issues.

• Explain that users need to click on the red X in the Qt interface to see the validation message
• Highlight that the changelog exists
• How to resolve common errors
• Factors that can cause a model to run slowly
• Etc

[phargogh]

A couple additional things that might be nice to add:

• How to save and load datastacks (and what a datastack is)
• What the n_workers parameter represents and when someone might want to use it (and what values to consider)