How to get Real-Time data

[machikoyasuda]

closes #451

What this PR does

• Adds /how-to/go-realtime link (This page is not yet added to the nav, so a user would not be able to find it from the website.)
• Adds text with links. (All links are done, except for links to the new page that has not been created yet "GTFS-Realtime Introduction" and to "GTFS-Realtime MSA Information Packet")
• Update link styles for all How To pages

Preview here: https://deploy-preview-617--cal-itp-mobility-marketplace.netlify.app/how-to/gtfs-rt

Design notes

• There are some design-changes on the general How To layout in Figma, that will not be reflected in this PR: The underlines in the TOC

[netlify]

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[machikoyasuda]

Preview link is here: https://deploy-preview-617--cal-itp-mobility-marketplace.netlify.app/how-to/gtfs-rt

The capitalization of gtfs-rt does not matter in the URL.