indextext.html: add notice about upcoming ssh host key change
Mention the upcoming SSH host key replacement on the home page to
hopefully minimize alarm.
The original SSH host key used for ssh repository access since the
beginning of repo.or.cz is no longer considered sufficiently secure
and must be replaced since the most recent ssh clients will generally
refuse to connect anymore in their default configuration.
Include details about the ugly message that will be shown by the
ssh client and the fingerprint of the new key that should match the
fingerprint shown in the ssh client's error message.
Signed-off-by: Kyle J. McKay <mackyle@gmail.com>