Add nsswitch.conf to FILES section of ipa-client-install man page

This file is always updated when client is installed or uninstalled.

https://fedorahosted.org/freeipa/ticket/3995

ipa-client/man/ipa-client-install.1

@@ -218,6 +218,7 @@ Files always created (replacing existing content):
 .TP
 Files updated, existing content is maintained:
 
+/etc/nsswitch.conf\p
 /etc/pki/nssdb\p
 /etc/krb5.keytab\p
 /etc/sysconfig/network\p