Uncomprehensible help message in install_desimodel_data

[rainwoodman]

Really tiny, but ....

"""
...
is, the directory specified by the environment variable. 2. The value set with
the -d option on the command line. 3. A directory relative to the file
containing this script. This directory is currently <function
default_install_dir at 0x2aaaac07b398>. If the data directory already exists,
this script will not do anything.
...
"""