Update bug_report.md

Author: mrdoob

.github/ISSUE_TEMPLATE/bug_report.md

@@ -7,6 +7,8 @@ assignees: ''
 
 ---
 
+<!-- Ignoring this template may result in your bug report getting deleted -->
+
 **Describe the bug**
 
 A clear and concise description of what the bug is. Before submitting, please remove unnecessary sections.