Doxygen-how to document files with non-standard extension (.INI)

I have a simple question: how do I document .INI file?

I have a C++ project with the following layout:

readme.txt
src
    main.cpp
data
    simple.ini

I have no problem generating document from readme.txt and main.cpp, but the document in simple.ini does not show in the html output at all. I have fixed the Doxygen file to include the following:

INPUT = . src data
FILE_PATTERNS = *.cpp *.txt *.ini

That did not help. I also explicitly specify simple.ini:

INPUT = readme.txt data/simple.ini src

But it did not work either. Within simple.ini, I use ';' for comment:

; @file simple.ini
; This file will do blah blah blah
[section1]
key1 = foo
key2 = bar
...

I also tried to use '#' for comment char, but it did not work, either. How do I make doxygen to process simple.ini?