[docs] Document gotchas around input element's `value` `checked` attribute

Nobody has claimed this yet.

It's easy for users to do an attribute binding with reactive properties for `value` or `checked` for `` elements instead of property bindings and expect them to update. Sometimes it feels like this works because the element does update based on the attribute until the user interacts with the element, at which point only changing the property updates the element.

Documenting this gotcha and suggestion to do a property binding with `.` would be nice.

Semi-related to this is wanting to reset the input value with a `requestUpdate()` after user interaction and not seeing it update which requires the `live()` directive.

No documentation file is named. Start by locating the input element binding guidance and the live() directive documentation, then explain the value and checked attribute-versus-property gotcha and when live() is needed after interaction. Done means both scenarios and the property-binding suggestion are clearly documented.

Written by the indexing model from the issue text.