Added help command for duckpan

[killerfish]

As commented in #166.

[moollaza]

Just commented in #166, but duckpan help already works for me as expected, though it isn't implemented as a specific Cmd. I believe that was by design so we could easily use it to show the help output for unknown commands.

This should be okay though because we're just telling them to use duckpan help now for unknown commands.

[killerfish]

@moollaza can you try with the latest build, because help wasnt working for me, apparently (no pod just the error msg), after i merged with the latest branch. The reason i mentioned in #166 made sense to me, so a bit curious, how help could trigger.

[moollaza]

@killerfish apologies, you're correct. I haven't released the latest changes yet but in Master because that line was removed, duckpan help no longer works.

[moollaza]

@killerfish this LGTM. I'm going to make another PR to build on this. Adds tests and fixed duckpan to also output the help info :)