Altered play command message as seen in 'help'

Thanks for all the work that everyone has put into making Pry such a great tool!!!

When reading the 'help' section during pair programming today, the 'play' method wasn't clear to me.

The `help play` gives a very clear explanation but I wouldn't have found that based on the short explanation given by `help`.

So, this tweak is a rough first stab at altering the message and helping others benefit from this awesome utility :)

PS - At the very least this PR can constitute a reminder that I'd like to revise the message to be more revealing :smile: .