[Form] Add examples for submitting PATCH requests without handleRequest()

[michaeljoelphillips]

Greetings,

I ran into a specific use case where a single page application was submitting a form to a REST API without a submit button via an HTTP PATCH method. I had read somewhere (probably StackOverflow) that handleRequest() handles partial updates since Symfony 2.x, but since there wasn't a submit button, handleRequest() wouldn't submit the form.

Long story short, I wasn't able to find documentation regarding a solution until I saw the API for the submit() function with the optional $clearMissing parameter. I'm willing to submit a PR with this use case highlighting the ability to do partial updates via the submit() function if it sounds useful to anyone else.

[HeahDude]

Good idea! 👍

[xabbuh]

Sounds like a good idea to me.

@Nomad145 We welcome every pull request that tries to improve the documentation. :)

[michaeljoelphillips]

Sweet! I'll see what I can do!