Update pakistan.html

Pakistan mailing list is now live, lets add it! :)
Yes, I think linking to a web page is better wherever possible. You can amend your previous commit with the new changes, and if you can make the commit message a bit more descriptive of this code change is about that would also be good. I suggest "Add mailing list to Pakistan community page"

Since you mention it, I'll update the India community page to link to https://lists.mozilla.org/listinfo/community-india. I'm sure there are others as well.