Update pakistan.html

Pakistan mailing list is now live, lets add it! :)
Should I really link to the info page rather than the email address?  I am just following other community's  template, like for India its:

https://www.mozilla.org/en-US/contact/communities/india/
https://github.com/swarnava/bedrock/blob/patch-3/bedrock/mozorg/templates/mozorg/contact/communities/india.html#L18