Update README.md to point to tutorials deployment instructions

[abbycross]

This adds a link from the README to the tutorials directory README, where instructions for tutorial files (deploying, adding, etc.) lives.

[abbycross]

FYI - All the URL changes I had made are because CI failed for detecting "bare" URLs.

[frankharkins]

Weird about prettier; maybe the version in CI has changed?

[Eric-Arellano]

Idk what was going on with the formatting. Replaced by https://github.com/Qiskit/documentation/pull/1450.