'add' and 'subtract' formatting discrepancy between docs and autofill

[mdroidian]

On the docs, both add and subtract formatting is presented with single curly braces: add({label1}, {label2})

https://github.com/RoamJS/query-builder/blob/main/docs/query-builder.md#supported-data-types
https://github.com/RoamJS/query-builder/blob/main/docs/examples.md#add-or-subtract

When auto-filled inside of the Query Builder as a selection, the formatting is double curly braces and brackets: add({{selection}},[###])

Reported by Chris H via slack