README: add nuance to description of git clone --depth
README: add nuance to description of git clone --depth

Closes #47
Suggested-by: Aleksander Nitecki

cnweibo/git-fat,grahamgilbert/git-fat,cnweibo/git-fat,jedbrown/git-fat,jedbrown/git-fat,wikimedia/operations-debs-git-fat,wikimedia/operations-debs-git-fat,grahamgilbert/git-fat