Docs: document apostrophe as an explicit string literal trigger

[sequba]

Description

By starting the cell content with ' character (apostrophe) our parser treats the rest of it as string. I cannot find any docs that mention this feature.

Links

https://github.com/handsontable/hyperformula/discussions/959 https://github.com/handsontable/hyperformula/blob/fd0a40581d1dea2a19c2307228825ad0c3b6dedb/test/CellContentParser.spec.ts#L128-L135

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