Update Extension FAQ to be more general questions and answers

[ghostbear]

Acknowledgements

• I have searched the existing issues and this is a new ticket, NOT a duplicate or related to another open issue.
• I have written a short but informative title.
• I will fill out all of the requested information in this form.

Describe your suggested feature

With extensions now being able to have their own FAQ and guides. The Extension FAQ should be updated to have more general question and answers that works for all extensions.

• Remove the sections about MangaDex, Mangakakalot, Manganelo, Mangabat, Mangairo and MangaPark
• Update Extension FAQ with general question and answers
• Mention that extensions can have their own FAQ and guides

Other details

No response