Add PIV factory reset

Author: mmerklinger

nitrokey3/windows/piv/factory_reset.rst

@@ -0,0 +1,14 @@
+Factory Reset
+=============
+
+The PIV application can be reset to factory defaults.
+It can only be reset if the PIN and PUK are blocked.
+
+.. warning::
+   Performing a factory reset of the PIV application will delete all private keys and certificates.
+
+The reset to factory defaults can be performed as follows.
+
+.. code-block::
+
+    nitropy nk3 piv factory-reset

nitrokey3/windows/piv/index.rst

@@ -14,4 +14,5 @@ The *Personal Identity Verfication* (PIV) is based on the NIST special publicati
 
    access_control.rst
    certificate_management.rst
+   factory_reset.rst
    guides/index.rst