Clarify that kdc.conf and krb5.conf are merged

These two files are merged into the profile for KDC applications

(cherry picked from commit e818d27a372d021bc6025e7bce867ed06a8fc1ad)

https://github.com/krb5/krb5/commit/f3c50244f6d6967dff4e3158408f71efb3a5c665
Author: Ben Kaduk <kaduk@mit.edu>
Committer: Tom Yu <tlyu@mit.edu>
Commit: f3c50244f6d6967dff4e3158408f71efb3a5c665
Branch: krb5-1.11
 doc/admin/conf_files/index.rst    |   11 +++++++++++
 doc/admin/conf_files/kdc_conf.rst |    4 +++-
 2 files changed, 14 insertions(+), 1 deletions(-)