/usr/share/doc/postfix-cdb/README.Debian is in postfix-cdb 3.3.0-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | The postfix-doc package contains documentation on how to configure this
map type. See /usr/share/doc/postfix/html/CDB_README.html
|