example: freeze & unfreeze

[bjuergens]

use-case:

• the data-folder is already part of the archive
• new data shall be added to the data folder
• the data is added by the projects itself (so the data must be unfrozen while the code is running)

related: #10

steps:

1. prepare example
2. unfreeze data (cp -al hashed_dir dir && update softlink)
   1 run code
3. re-freeze data (dirhash --move-to-archive --softlink )