Summary:

This PR adds hyperlinks to the "Help" and "Contact Us" buttons in the top bar of the index website:

Right now here are the hyperlinks, although these can be changed:

• Help -> https://github.com/MobilityData/gtfs-realtime-validator/blob/master/TROUBLESHOOTING.md
• Contact Us -> https://bit.ly/mobilitydata-slack

This PR also removes the "About" menu item, as that is ticketed separately in #52 with some work towards it in #84.

Closes #50.

Expected behavior:

Currently when clicking "Help" and "Contact Us" nothing happens. This PR adds hyperlinks to both.

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