define django log file in environment variable

README.md

 export DJANGO_SECRET_KEY="xxx"
 export DJANGO_PRODUCTION_DOMAIN="xxx"
 
+# log file
+export DJANGO_LOG_FILE="xxx"
+
 # static and media files dir in production
 export DJANGO_STATIC_ROOT="xxx"
 export DJANGO_MEDIA_ROOT="xxx"

tickets/settings.py

         'file': {
             'level': 'INFO',
             'class': 'logging.FileHandler',
-            'filename': '../logs/django-tickets.log',
+            'filename': os.environ["DJANGO_LOG_FILE"],
             'formatter': 'verbose'
         },
         'mail_admins': {