docs: Update broken docs link in Readme

[fredcarle]

Relevant issue(s)

Resolves #4116

Description

This PR fixes a link where the path to the docs was missing /defradb in the path.

[AndrewSisley]

LGTM, thanks Fred

[dmjlya]

LGTM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.26%. Comparing base (e874405) to head (ee7e2e8).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4117      +/-   ##
===========================================
- Coverage    77.28%   77.26%   -0.02%     
===========================================
  Files          482      482              
  Lines        37263    37263              
===========================================
- Hits         28798    28791       -7     
- Misses        6192     6199       +7     
  Partials      2273     2273              

Flag	Coverage Δ
all-tests	77.26% <ø> (-0.02%)	⬇️

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see 6 files with indirect coverage changes

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