Replace input table

[BD103]

This closes #34.

This PR:

• Replaces the inputs and outputs tables in the README.md to be a code block and a bulleted list, respectively.
  • I wasn't sure how to document outputs in code, so I used a bulleted list instead.
  • Note that cache-hit can be "true", "false", or "", depending on the scenario, so I modified our description to say it is a string instead of a boolean. Check out the docs for why this is.
• Improved the descriptions of all inputs and outputs to be consistent, and synchronized them across action.yml and README.md.
  • I removed explicit writing that said "Defaults to value", as the default is always documented nearby. Tell me what you think!
• Fixed a bug where the cache-hit output would never be true.
  • It set its value to ${{ steps.cache.outputs.random-number }}, not ${{ steps.cache.outputs.cache-hit }}.