Update Installing_OCSP_with_HSM.adoc

[skip ci]
added Prerequisites

docs/installation/ocsp/Installing_OCSP_with_HSM.adoc

@@ -1,11 +1,15 @@
 = Installing OCSP with HSM =
 
-Overview
---------
-
+== Overview  
 This page describes the process to install an OCSP subsystem
 where the system certificates and their keys will be stored in HSM.
 
+== Prerequisites ==
+Prior to installation, please ensure that the following are configured:
+
+* link:../others/FQDN_Configuration.adoc[Setting the FQDN of the host system]
+* link:../others/Creating_DS_instance.adoc[Creating a directory server instance and adding base entries]
+
 == OCSP Subsystem Installation ==
 
 Prepare a file (e.g. ocsp.cfg) that contains the deployment configuration, for example: