docs(i): Replace broken DQL link in README

[amarkpark]

Relevant issue(s)

Resolves #3269

Description

This is a change to update a broken link in the README.
This changes the target URI to point to an extant page in the docs.
FROM:
https://docs.source.network/references/query-specification/query-language-overview
TO:
https://docs.source.network/defradb/references/query-specification/query-language-overview

NO CODE CHANGES

Tasks

• [NA] I made sure the code is well commented, particularly hard-to-understand areas.
• I made sure the repository-held documentation is changed accordingly.
• I made sure the pull request title adheres to the conventional commit style (the subset used in the project can be found in tools/configs/chglog/config.yml).
• [NA] I made sure to discuss its limitations such as threats to validity, vulnerability to mistake and misuse, robustness to invalidation of assumptions, resource requirements, ...

How has this been tested?

I manually followed the old link and the new link. Old was a broken link. New is a proposed correct link.

Specify the platform(s) on which this was tested:

• MacOS

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.04%. Comparing base (c7b8b93) to head (0d1258d).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3274      +/-   ##
===========================================
- Coverage    78.09%   78.04%   -0.05%     
===========================================
  Files          382      382              
  Lines        35364    35364              
===========================================
- Hits         27615    27599      -16     
- Misses        6116     6126      +10     
- Partials      1633     1639       +6     

Flag	Coverage Δ
all-tests	78.04% <ø> (-0.05%)	⬇️

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see 15 files with indirect coverage changes

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