chore(PULL_REQUEST_TEMPLATE): require MDN compat data for PRs

Author: marcoscaceres

.github/PULL_REQUEST_TEMPLATE.md

@@ -5,6 +5,7 @@ The following tasks have been completed:
  * [ ] Confirmed there are no ReSpec errors/warnings.
  * [ ] Added Web platform tests (link)
  * [ ] added MDN Docs (link)
+ * [ ] added MDN [compat data](https://github.com/mdn/browser-compat-data)
 
 Implementation commitment:
 
@@ -13,4 +14,4 @@ Implementation commitment:
  * [ ] Firefox (link to issue)
  * [ ] Edge (public signal)
 
-Impact on Payment Handler spec? 
+Impact on Payment Handler spec?