How to create TWRP's data.info file by hand/after the backup?
to answer the headline, there exist a little shell script twrp_sign.sh for generating data.info and sha2 digest. you can open it with text editor and see how it works  

data.info is just a string containing
archive_name
backup_size
file_count
backup_type  

Note: only the .win* files are important, all other files can be safely deleted without data loss