Add YouthMappers chapters

[quincylvania]

Closes #152.

I wrote a script to convert the spreadsheet from @Geocruizer into the format for this index.

• The GeoJSON features are circles with a 25 km (15.5 mi) radius around the school.
• Not all chapters have URLs. For these there are mailto: links to the contact email instead.
• There are no contact names, which I think is okay since these are school groups that may have high turnover.
• Updated information can be submitted manually, like for other entries in this index.
• We could add a youthmappers resource type to the index if we had an SVG of the logo.

[quincylvania]

I added the logo and the resource type so this should be good to go!

[bhousel]

Looks great! feel free to merge 👍