Improve formatting of the README

[chadoh]

I found it very difficult to comprehend the README as it was written. I think better formatting is mostly all it needs.

Here's what I did:

• Switched it to Markdown, instead of just text
• Put long lines all on one line, to allow Github to wrap them optimally
• Replaced tabs with two spaces
• Made headers, code examples, etc use Markdown format

[plentz]

+1

[wpp]

I agree. The formatting IMO would improve the README significantly.

[ashoda]

+1

[phoet]

@plentz 👋 you find those shopifolk everywhere! doesnt look like this is maintained? leaving this PR here though https://github.com/rubyredrick/ri_cal/pull/22