Meta: add issue template for WHATNOT meetings

Co-authored-by: Chris Wilson <cwilso@gmail.com>
Co-authored-by: sideshowbarker <mike@w3.org>

Author: 3 people

.github/ISSUE_TEMPLATE/upcoming-whatnot-meeting.md

@@ -0,0 +1,14 @@
+---
+name: Upcoming WHATNOT meeting
+about: Create a new WHATNOT meeting announcement
+title: Upcoming WHATNOT meeting on 20YY-MM-DD
+labels: agenda+
+---
+
+Today we held our weekly triage call, see [LINK TO PREVIOUS AGENDA ISSUE], and the meeting notes have been posted there.
+
+[DELETE ONE OF THE FOLLOWING TWO LINES AND FILL IN THE DATE]
+The next one is scheduled for [DATE], at 9AM PT. Note that this is 1 week later in the AMER-EMEA friendly time.
+The next one is scheduled for [DATE], at 10AM CE(S)T. Note that this is 1 week later in the APAC-EMEA friendly time.
+
+People interested in attending the next call who need the invite: Please respond here or reach out on [Chat](https://whatwg.org/chat). Please tag issues and PRs for the next call using agenda+ in all WHATWG repositories across [issues](https://github.com/search?q=org%3Awhatwg+is%3Aopen+label%3Aagenda%2B&type=issues) and [pull requests](https://github.com/search?q=org%3Awhatwg+is%3Aopen+label%3Aagenda%2B&type=pullrequests). We invite anyone who can contribute to join us.