Add http://localhost:8111/help

[jidanni]

Add ​http://localhost:8111/help .
That way one need not trigger an HTTP error when wanting to read the
help output.

$ w3m -dump http://localhost:8111/
HTTP Error 400: Bad Request

No command specified! The following commands are available:

  • /add_node — adds a node (given by its latitude and longitude) to the current dataset
...

[stoecker]

As we still would need to output the same text for invalid requests a help call has no benefit, especially as this is only interesting for developers.