add robots.txt file

[louking]

getting lots of exceptions from bots trying to access /route/turns or other such nonsense

• https://stackoverflow.com/a/14625619/799921
• https://support.google.com/webmasters/answer/6062608?hl=en

e.g., from google bot:

        Message type:       ERROR
        Location:           /var/www/www.routes.loutilities.com/venv/lib64/python3.6/site-packages/flask/app.py:1891
        Module:             app
        Function:           log_exception
        Time:               2020-10-21 13:47:34,708

        Message:

        Exception on /turns/routes [GET]

Traceback (most recent call last):
  File "/var/www/www.routes.loutilities.com/venv/lib64/python3.6/site-packages/flask/app.py", line 2446, in wsgi_app
    response = self.full_dispatch_request()
  File "/var/www/www.routes.loutilities.com/venv/lib64/python3.6/site-packages/flask/app.py", line 1951, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/var/www/www.routes.loutilities.com/venv/lib64/python3.6/site-packages/flask/app.py", line 1820, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/var/www/www.routes.loutilities.com/venv/lib64/python3.6/site-packages/flask/_compat.py", line 39, in reraise
    raise value
  File "/var/www/www.routes.loutilities.com/venv/lib64/python3.6/site-packages/flask/app.py", line 1949, in full_dispatch_request
    rv = self.dispatch_request()
  File "/var/www/www.routes.loutilities.com/venv/lib64/python3.6/site-packages/flask/app.py", line 1935, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/var/www/www.routes.loutilities.com/venv/lib64/python3.6/site-packages/flask/views.py", line 89, in view
    return self.dispatch_request(*args, **kwargs)
  File "/var/www/www.routes.loutilities.com/venv/lib64/python3.6/site-packages/flask/views.py", line 163, in dispatch_request
    return meth(*args, **kwargs)
  File "/var/www/www.routes.loutilities.com/runningroutes/runningroutes/runningroutes/views/frontend/frontend.py", line 292, in get
    return self._renderpage(thisid)
  File "/var/www/www.routes.loutilities.com/runningroutes/runningroutes/runningroutes/views/frontend/frontend.py", line 298, in _renderpage
    thisid = int(thisid)
ValueError: invalid literal for int() with base 10: 'routes'