Add tips for Supervisor user

[greyli]

When configuring Supervisor program to run with Pipenv, for example:

[program:bluelog]
command=pipenv run gunicorn -w 4 wsgi:app
directory=/home/greyli/bluelog
user=greyli

You will get Click's RuntimeError due to the locale issue:

supervisor> tail bluelog stderr
n(*args, **kwargs)
  File "/usr/local/lib/python3.5/dist-packages/pipenv/vendor/click/core.py", line 676, in main
    _verify_python3_env()
  File "/usr/local/lib/python3.5/dist-packages/pipenv/vendor/click/_unicodefun.py", line 118, in _verify_python3_env
    'for mitigation steps.' + extra)
RuntimeError: Click will abort further execution because Python 3 was configured to use ASCII as encoding for the environment.  Consult http://click.pocoo.org/python3/for mitigation steps.

This system supports the C.UTF-8 locale which is recommended.
You might be able to resolve your issue by exporting the
following environment variables:

    export LC_ALL=C.UTF-8
    export LANG=C.UTF-8

It can be fixed by adding enviroment setting in Supervisor's config file:

[supervisord]
environment=LC_ALL='en_US.UTF-8',LANG='en_US.UTF-8'

[kennethreitz]

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