docs: update broken readme links

[srtaalej]

Summary

This PR updates broken links in the README.md.

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.09%. Comparing base (bb284c6) to head (ea3a80e).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2466   +/-   ##
=======================================
  Coverage   93.09%   93.09%           
=======================================
  Files          40       40           
  Lines       11240    11240           
  Branches      713      713           
=======================================
  Hits        10464    10464           
  Misses        764      764           
  Partials       12       12           

Flag	Coverage Δ
cli-hooks	95.23% <ø> (ø)
cli-test	94.79% <ø> (ø)
oauth	77.39% <ø> (ø)
socket-mode	61.87% <ø> (ø)
web-api	98.11% <ø> (ø)
webhook	96.66% <ø> (ø)

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