Update target_repo_dir docstring
See
MODIFY
repo2docker/app.py
repo2docker/app.py
@@ -354,7 +354,8 @@ class Repo2Docker(Application):
target_repo_dir = Unicode(
"",
help="""
- Path inside the image where contents of the repositories are copied to.
+ Path inside the image where contents of the repositories are copied to,
+ and where all the build operations (such as postBuild) happen.
Defaults to ${HOME} if not set
""",

Update target_repo_dir docstring

See https://discourse.jupyter.org/t/users-home-in-jupyterhub/1463/3