Documentation on how to disable introspection

[nicastelo]

Hi! I wanted to disable introspection but all I found in the docs was how to put it behind authentication. I found you can completely disable it by doing GraphqlDevise::Schema.disable_introspection_entry_points, so I added some documentation about it. Hope this is something you want to document.

Changes Made

• Added a new section, Disable Introspection, explaining how to completely disable introspection entry points using the disable_introspection_entry_points method.
• Updated the Introspection query section to include a reference to the new Disable Introspection section for users who want to completely disable introspection queries.

[mcelicalderon]

Hey, @nicastelo! Thank you for your contribution. We need to look into compatibility for graphql versions, but I don't see a reason why we shouldn't add guidance like this. I'll look into this tomorrow