Merge pull request #5821 from AvaloniaUI/danwalmsley-patch-1

Update PULL_REQUEST_TEMPLATE.md

Author: danwalmsley

.github/PULL_REQUEST_TEMPLATE.md

@@ -23,6 +23,8 @@
 ## Breaking changes
 <!--- List any breaking changes here. When the PR is merged please add an entry to https://github.com/AvaloniaUI/Avalonia/wiki/Breaking-Changes -->
 
+## Obsoletions / Deprecations
+<!--- Obsolete and Deprecated attributes on APIs MUST only be included when discussed with Core team. @grokys, @kekekeks & @danwalmsley -->
 
 ## Fixed issues
 <!--- If the pull request fixes issue(s) list them like this: