Improve project documentation

[Swiddis]

WIP PR for making more info about the bot available:

• [x] Help command per #6
  • [x] Document main commands
  • [x] Add command to list store items (Partially done)
• [x] Better README
  • [X] Badges
  • [x] Improved description/introduction
  • [x] Better contribution guidelines (formalizing meaning of "help wanted" and "good first issue" labels, expectations with testing)

Closes #6

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (0ab4fe6) 79.47% compared to head (9aba2a7) 80.74%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #32 +/- ## ========================================== + Coverage 79.47% 80.74% +1.26% ========================================== Files 10 10 Lines 307 296 -11 ========================================== - Hits 244 239 -5 + Misses 63 57 -6 ```

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[Swiddis]

Marking as ready for review preliminarily. Store listing isn't a separate command but the functionality is there nonetheless, store can be a separate PR.