Read a packed archive (.pack) from the standard input, expanding
the objects contained within and writing them into the repository in
"loose" (one object per file) format.
Objects that already exist in the repository will not be unpacked
from the packfile. Therefore, nothing will be unpacked if you use
this command on a packfile that exists within the target repository.
See git-repack(1) for options to generate
new packs and replace existing ones.