Provide the directory in from which templates will be used.
+ Specify that the git repository is to be shared amongst several users.
environment variable then the sha1 directories are created underneath -
otherwise the default `$GIT_DIR/objects` directory is used.
-`git-init-db` won't hurt an existing repository.
+A shared repository allows users belonging to the same group to push into that
+repository. When specifying `--shared` the config variable "core.sharedRepository"
+is set to 'true' so that directories under `$GIT_DIR` are made group writable
+(and g+sx, since the git group may be not the primary group of all users).
+Running `git-init-db` in an existing repository is safe. It will not overwrite
+things that are already there. The primary reason for rerunning `git-init-db`
+is to pick up newly added templates.