toolbox: note an issue I found trying to build the centos toolbox

The "fake" name used in the image only works if you build the container
locally first or are running in our CI. Since this is not a good general
solution, I put a comment here as a reminder it should be fixed later.

Signed-off-by: John Mulligan <[email protected]>

images/toolbox/Containerfile.centos

@@ -1,3 +1,8 @@
+# FIXME - this is not a real tag publicly available in the
+# quay.io/samba.org/samba-client repository. This only works if you build
+# the centos client locally first or acquire the image from a side channel.
+# This needs to be converted to something public and/or configurable
+# later.
 FROM quay.io/samba.org/samba-client:centos-latest
 MAINTAINER Shachar Sharon <[email protected]>