Clarify KJ method card

[awfrancisco]

The language in the KJ method should be edited to be more useful to new users. There are two main issues

• The name "KJ method" is a jargon term and may be off-putting to users who are unfamiliar with it
• The method is similar to the affinity diagramming card in a the Decide section. It is correct for there to be two different cards since these methods are substantially different, but the KJ method card should be edited to reference affinity diagramming and highlight why it's important to use this method in the discover phase.

[colinpmacarthur]

Added to a Trello card, so I'm going to close for now.