Update description to prefer the exploit module

Author: wvu

modules/auxiliary/scanner/http/apache_mod_cgi_bash_env.rb

@@ -22,6 +22,10 @@ def initialize(info = {})
         PROTIP: Use exploit/multi/handler with a PAYLOAD appropriate to your
         CMD, set ExitOnSession false, run -j, and then run this module to create
         sessions on vulnerable hosts.
+
+        Note that this is not the recommended method for obtaining shells.
+        If you require sessions, please use the apache_mod_cgi_bash_env_exec
+        exploit module instead.
       },
       'Author' => [
         'Stephane Chazelas', # Vulnerability discovery