Add missing @Flag initializer in example

[cg-soft]

The documentation as presented doesn't compile. An initializer is required for a boolean flag.

rdar://132579907

Checklist

• I've added at least one test that validates that my change is working, if appropriate
• I've followed the code style of the rest of the project
• I've read the Contribution Guidelines
• I've updated the documentation if necessary

[rauhul]

I can't remember if omitting the initial value is intended to work, @natecook1000 do you recall?

[cg-soft]

@rauhul it definitely does not work. Leaving out the initial value makes it assume it's an Int, and I get this error:

error: property type 'Bool' does not match 'wrappedValue' type 'Int'
    var verbose: Bool
        ^~~~~~~

[natecook1000]

Right! I think you can only omit the default false value when you specify an inversion (like a --foo/--no-foo pair), which makes specifying one of those values required.

[natecook1000]

@swift-ci Please test