Document `--` to support all remaining command line args as Arguments

[thomasvl]

Looks like some of the tests already confirm it, but the documentation doesn't seem to call out that the library does support the standard of taking an -- argument to then map all following command line args to be Arguments (and never recognize them as Flags/Options).

[natecook1000]

We really should cover all the different kinds of syntax that are allowed, such as grouped short options and --option=value style options. May be good to say what isn't currently supported as well, like -j5 style short options.

[thomasvl]

When I filed this, I was thinking the Markdown docs on the site; but thinking about it again, the generated help might also need to include some more details about things like this too.

[Rish-it]

@thomasvl claim

[EngOmarElsayed]

Can I work on this issue @natecook1000