improve high impact sketch on intro page

[mikofski]

@melissawm suggested in #60 that this might render better:

                              |
                              |
             🍎               |               ✅
                              |
        High Impact,          |          High Impact,
                              |
        Low Effort            |          High Effort
                              |
                              |
— — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — 
                              |
                              |
                              |
         Low Impact,          |           Low Impact,
                              |
         Low Effort           |           High Effort
                              |
                              |

[noatamir]

To do:

• create new graphic
• check how the emojis are described by screen readers
• create a description for the graphic, matching those descriptions