Merge pull request PrestaShop#41585 from PrestaShop/pr-security-warning

Update pull request template

Author: kpodemski

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,3 +1,14 @@
+<!-----------------------------------------------------------------------------
+⚠️ SECURITY WARNING — READ BEFORE OPENING THIS PULL REQUEST ⚠️
+
+If this pull request fixes or relates to a SECURITY vulnerability, DO NOT open
+it here. Public pull requests disclose the vulnerability to everyone, including
+attackers, before a fix is released.
+
+Please report security issues privately by contacting
+security-core@prestashop.com instead.
+------------------------------------------------------------------------------>
+
 <!-----------------------------------------------------------------------------
 Thank you for contributing to the PrestaShop project!