Feature: get instances.social link included in Mastodon

[AMDphreak]

Mastodon is supposed to connect people. How can people feel connected when they're unaware that Mastodon has many instances? Mastodon can't hope to ever grow when it does not make it obvious to new users that they are signing up and seeing just a single instance. The interconnected nature of Mastodon instances should be an integral part of the browsing experience. A map of Mastodon instances should be included in the Mastodon interface at the top, providing a top-down overview of the Mastodon communities.