feat: improve doc with viewcontroller

[anthony-bernardo]

Hi,

I'm struggling to create a plugin with ios. Despite the documentation https://capacitorjs.com/docs/plugins/ios, I cannot run a plugin that present a new viewController. I tried with storyboard (inside the plugin), with xib files, but I cannot reach the goal.

I opened a stackoverflow https://stackoverflow.com/questions/64693531/new-view-in-ios-with-capacitor-plugin

I think it would be great to improve the doc, with an example with a xib and storboard file. Because not all capacitor developpers know very well the ios native development (this is my case)

Or if usage of storyboard or xib is not possible in a plugin, then mention it in documentation