Tried here both html and a file placed in disk (/tmp folder), but didn't work.
I noticed that the Resources folder has the following structure:
-rw-r-xr-x 18:34 background
drwxr-xr-x 17:12 de.lproj
drwxr-xr-x 17:14 en.lproj
The readme files are inside de.lproj and en.lproj.
I also tried to copy these folder inside /tmp/ and change distribution to <readme file="/tmp/readme.rtf"/>. Not surprised it didn't work.