Print error if list and item share a name

[thenickcox]

First, thanks for this. I love it, and find it useful to save snippets of commonly used reaction gifs to paste into Slack at work.

But I ran into this issue.

Example:

➜  ~ boom foo
Boom! Created a new list called foo.
➜  ~ boom bar
Boom! Created a new list called bar.
➜  ~ boom foo bar http://google.com
Boom! bar in foo is http://google.com. Got it.
➜  ~ boom bar
➜  ~ 

I ran into this a few times and couldn't figure out why it would just return with no output. It'd be great to say something like:

Boom! We found both a list an an item with the name $NAME. To access the item, prepend its list name.

Is this something you'd think about accepting a PR for?