Add link to official Ruby on Rails Mastodon account

[mlcohen]

Update the Ruby on Rails homepage to include a link to the new official Ruby on Rails Mastodon account -- @[email protected]

Details

• Added a mastodon icon that was taken from here https://joinmastodon.org/branding
• Link to Mastodon account includes a rel="me" attribute which is needed to properly verify the account
• Updated Scss to adjust margins

Related issue: rails/rails#50074

Before: Without Mastodon link

After: With Mastodon link

(running on local machine)

[AmandaPerino]

Hi! Please see my comment on Issue 50074.
We truly appreciate the suggestion, but won't be posting on Mastodon (or other new social media sites) at this time.