Docs: Make it clear that text values inside formulas need to be enclosed in double quotes

[sequba]

Description

Our users ask about it

Links

https://handsoncode.slack.com/archives/C031GBX62SE/p1668695428147239 (internal discussion)

Type of issue

• [x] Missing documentation
• [ ] Error in the documentation
• [ ] Request for a demo
• [ ] Request for a tutorial, guide etc.
• [ ] Other issues, suggestions or ideas