document what 'tahoe cp' does with trailing slashes

[davidsarah]

The --help text for tahoe cp says:

... Arguments should probably not have trailing slashes.
'tahoe cp' does not behave as much like /bin/cp as you
would wish, especially with respect to trailing slashes.

But this doesn't tell me how tahoe cp behaves with trailing slashes, and I also don't know how /bin/cp behaves with trailing slashes, so I don't know whether that is the behaviour I would want.

I looked at man cp on Linux to see how it documented cp's behaviour with trailing slashes, and it didn't say, apart from documenting this option:

   --strip-trailing-slashes
          remove any trailing slashes from each SOURCE argument

[marlowe]

This covers the behaviour of the trailing slashes.

​http://tongtao.com/blog/?p=386

[daira]

Is this sufficiently documented by docs/frontends/CLI.rst@aa65426a​ line 461 ("Trailing slashes indicate directories, but are not required.")?

[warner]

I think so, yeah.