Add Documentation for DioxusFormattable Trait

[vitordeoliveira]

Currently, the DioxusFormattable trait in Dioxus lacks official documentation. This trait is useful for custom types that need to be formatted as strings within the framework.

In my use case, I created a wrapper struct Icon around Asset and implemented DioxusFormattable for it. This allows Icon instances to be used seamlessly as formatted strings in components.

Example usage:

#[derive(PartialEq, Props, Clone)]
pub struct MenuProps {
    icon: Icon,
    children: Element,
    #[props(into)]
    to: NavigationTarget,
}

#[component]
pub fn ManuLink(props: MenuProps) -> Element {
    let MenuProps { to, children, icon } = props;
    rsx! {
        Link {
            to,
            div {
                class: "flex items-center gap-8 p-5 rounded hover:bg-secondary-darker",
                img {src: icon}
                {children}
            }
        }
    }
}

Adding documentation for DioxusFormattable would help developers understand its purpose, usage, and best practices for implementing it in their own projects.