[DISCUSS] add notifications mailing list

[PJ Fanning]

I think this mailing list is being swamped in automated emails from GitHub. I 
think I will have to unsubscribe because I am involved in multiple projects and 
I can't have dozens of mails coming in about Texera PRs every day.
My preference would be to have Texera set up a notifications mailing list where 
we can redirect the GitHub emails. This would mean that this list could be kept 
for real emails that discuss dev matters.