Updates rescript syntax in docs

[EthanBonsignori]

Hi there 👋

I was reading the docs and noticed some syntax was out of date so I made a few changes that do the following:

1. replaces type wrappers using () with <> option('type) -> option<'type>
2. changes form ppx extension syntax with from being wrapped in [] to wrapping with (): [%form ...]; -> %form(...)
3. removes [] from wrapping attributes: [@react.component] -> @react.component
   and with args i.e. an input type: [field]: @field.async(mode: OnBlur) string,
4. adds the rec keyword where missing to type examples that are followed by and type = ...

I took into account #119 and did not make the same changes they already did

[alex35mil]

@EthanBonsignori Sorry, I missed your PR either. Thank you!