Add link to XSA tracker

project-security/qsb.md

@@ -17,6 +17,7 @@ A **Qubes security bulletin (QSB)** is a security announcement issued by the
 [Qubes security team](/security/#qubes-security-team) through the [Qubes
 security pack](/security/pack/). A QSB typically provides a summary and impact
 analysis of one or more recently-discovered software vulnerabilities, including
-details about patching to address them.
+details about patching to address them. For Xen Security Advisories (XSAs), see
+the [XSA tracker](/security/xsa/).
 
 ## Full list