Documentation Update: Multiselect (checkboxes to checkbox) and General Doc Updates

[theperfectwill]

@ https://www.ultimate-fields.com/docs/fields/multiselect/

Needs checkboxes updated to checkbox.

See screenshot below.

As a NOTE: It seems maybe like a text replace search just didn't include the text within the code highlighted through the documentation. I've noticed little inconsistencies, so maybe that is the case, that I could wrap my head towards.

[theperfectwill]

Just to add complete context, using checkboxes returned nothing, meaning the default Select2 multiselect was returned. The default properties.