Add additional manga websites in mangadownloader

[senthilkumar1729]

Right now manga downloader only supports

https://www.mangapanda.com

It would be useful if more websites are added to the list , for example:

https://mangarock.com/

http://fanfox.net/

https://www.mangareader.net/

[RodolfoFerro]

Hey, I worked in this repo with Manga Fox by adding a downloader based on the one already done.

I'm hitting up a PR now.
#Hacktoberfest 🚀

[RodolfoFerro]

Done: #23

Do I need to update the README file for contributions?

[ionicc]

#23 Merged. You don't need to update the README, It will get updated automatically 😄.
Have fun and keep contribution ❤️