doc: add Utimaco SecurityServer HSM

Thanks to Rick van Rein <rick@openfortress.nl>!

doc/appendices.rst

@@ -69,6 +69,15 @@ support.
      - |yes|
      - |yes|
      - |yes|
+   * - `Utimaco SecurityServer (V4) <https://hsm.utimaco.com/products-hardware-security-modules/general-purpose-hsm/securityserver-cse/>`_ [#fn-utimaco]_
+     - |yes|
+     - |yes|
+     - |no|
+     - |yes|
+     - |yes|
+     - |yes|
+     - |yes|
+     - |yes|
 
 .. in progress: key ID checks have to be disabled in code
    * - `Yubikey NEO <https://www.yubico.com/products/yubikey-hardware/yubikey-neo/>`_
@@ -81,6 +90,8 @@ support.
      - |yes|
      - |no|
 
+.. [#fn-utimaco] Requires setting the number of background workers to 1!
+
 The following table summarizes supported DNSSEC algorithm numbers and minimal
 GnuTLS library version required. Any algorithm may work with older library,
 however the supported operations may be limited (e.g. private key import).