/etc/dnsmasq.d/README is in dnsmasq 2.76-5+deb9u2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 | # All files in this directory will be read by dnsmasq as
# configuration files, except if their names end in
# ".dpkg-dist",".dpkg-old" or ".dpkg-new"
#
# This can be changed by editing /etc/default/dnsmasq
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