DOC: Visual description of each symbol

[westurner]

A written description of each symbol in the README table could be helpful for training and memory purposes.

I wrote this; please feel free to reuse none or any of it without attribution:

Each of the symbols are drawn within a triangle pointing up:

• Immediate Help Needed (orange; downward triangle \n SOS),
• Shelter Needed (cyan; like a guy standing in a tall pentagon without a floor),
• OK: No Help Needed (green; upward triangle \n OK),
• First Aid Kit Needed (yellow; briefcase with a first aid cross),
• Water Needed (blue; rain droplet),
• Area with Children in Need (lilac; baby looking thing with a diaper on),
• Food Needed (red; pan with wheat drawn above it),
• Area with Elderly in Need (purple; person with a cane)

[krook]

Thanks for the contribution @westurner! I've updated the README and listed you as a contributor.

[westurner]

Thanks!