Document how to define a named expression on HyperFormula initialization

[sequba]

Description

There are 2 ways of defining named expressions:

• addNamedExpression() function
• the last argument of functions buildEmpty(), buildFromArray() & buildFromSheets()

const engine = HyperFormula.buildFromArray(
  [['=FOO']],
  {},
  [{ name: 'FOO', expression: '=42' }]
)

The latter way is documented poorly, there are no examples in the docs and there are no unit tests.

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