Adds a topic request issue generator

This will assist with helping others propose new topics.

Author: cjdb

.github/ISSUE_TEMPLATE/topic-proposal.md

@@ -0,0 +1,10 @@
+---
+name: Topic proposal
+about: Describes a topic that should be considered by SG20 for education guidelines
+title: "[TOPIC-REQUEST]"
+labels: Needs triaging
+assignees: BobSteagall, cjdb, jcvw
+
+---
+
+