Only NTP sources can be specified in the /etc/chrony/sources.d directory.
Files in this directory must end with the ".sources" suffix, and can only
contain the "peer", "pool" and "server" directives.

There is no need to restart chronyd for these time sources to be usable,
running 'chronyc reload sources' is sufficient.

Example:

# echo 'server 192.0.2.1 iburst' > /etc/chrony/sources.d/local-ntp-server.sources
# chronyc reload sources