Document krb5_get_init_creds_opt_set_in_ccache

More specifically, document that this new API was first
introduced in 1.11

(cherry picked from commit 63a344b05fb2543059c1049c93e3106a0c6aa853)

https://github.com/krb5/krb5/commit/d5d97dbffc9b63f7b8cc0ecddda6ade315de9d10
Author: Zhanna Tsitkov <tsitkova@mit.edu>
Committer: Tom Yu <tlyu@mit.edu>
Commit: d5d97dbffc9b63f7b8cc0ecddda6ade315de9d10
Branch: krb5-1.11
 src/include/krb5/krb5.hin |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)