[Doc] Mention that boolean properties require the dynamic syntax

[javiereguiluz]

Q	A
Bug fix?	no
New feature?	no
Issues	-
License	MIT

This confused me. On Symfony Slack folks mentioned that changing this behavior would be bad for DX (e.g. we can do it in components backend by a PHP class with typed properties but we cannot for anonymous components). So, I think it might be enough to mention this in the docs. Thanks.

[Kocal]

That's remind this ESLint rule for Vue.js: https://eslint.vuejs.org/rules/no-boolean-default

Ideally when you conceive your component, you don't want to use boolean props with a default value to true, to enforce HTML standard.

Depending on whether or not you want your close button to be displayed by default, you will need to have a property withCloseButton or withoutCloseButton default to false, meaning that you can simply use a prop with the static syntax like this:

<twig:Alert message="..." withCloseButton/>

<twig:Alert message="..." withoutCloseButton />

[kbond]

Thanks Javier.