add new SSVC rule in documentation

Signed-off-by: tdruez <tdruez@aboutcode.org>

Author: tdruez

docs/reference-vulnerability-triage.rst

@@ -19,7 +19,7 @@ that are relevant to its security program via the **Admin** interface.
 1. Built-in Rules
 -----------------
 
-Seven rules are available out of the box. Each rule implements a specific detection
+Eight rules are available out of the box. Each rule implements a specific detection
 condition evaluated against the vulnerabilities known to affect the product's packages.
 
 .. list-table::
@@ -40,6 +40,11 @@ condition evaluated against the vulnerabilities known to affect the product's pa
        | ``exploited_vulnerability``
      - Detects vulnerabilities for which a known active exploit is available
        (exploitability value equals 2.0).
+   * - | **SSVC Decision**
+       | ``ssvc_decision``
+     - Detects vulnerabilities whose `SSVC <https://www.cisa.gov/ssvc-calculator>`_
+       decision tree recommends **Attend** or **Act** (immediate attention required).
+       Matches if any of the vulnerability's published SSVC trees meets this threshold.
    * - | **Reachable Vulnerability**
        | ``reachable_vulnerability``
      - Detects vulnerabilities confirmed as reachable in the product context: at least