[ci skip] Add ffi_parser.c info

Author: petk

CONTRIBUTING.md

@@ -156,6 +156,9 @@ locations.
           ├─ parse_iso_intervals.c  # Generated by re2c 0.15.3
           └─ ...
        └─ ...
+    └─ ffi/
+       ├─ ffi_parser.c              # Generated by https://github.com/dstogov/llk
+       └─ ...
     └─ fileinfo/
        ├─ libmagic/                 # Modified libmagic https://github.com/file/file
        ├─ data_file.c               # Generated by `ext/fileinfo/create_data_file.php`