Fix redis links in README.md

[IvanVas]

Pull Request check-list

• Do tests and lints pass with this change?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• N/A Is there an example added to the examples folder (if applicable)?

Description of change

Fixes old redis.io links in README.md, uses valkey doc instead.

[bogdanp05]

Looks good, thanks for the fix

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.17%. Comparing base (12004ca) to head (67faad3).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #196      +/-   ##
==========================================
- Coverage   76.17%   76.17%   -0.01%     
==========================================
  Files         130      130              
  Lines       33983    33983              
==========================================
- Hits        25888    25886       -2     
- Misses       8095     8097       +2     

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