docs: Fix broken CometBFT installation guide link

[andreidavid]

Describe your changes

Updates the broken CometBFT installation guide link in README.md from /docs/guides/install.md to /docs/tutorials/install.md to ensure users can properly access the installation instructions.

Fixes #4006

Checklist before merging

• If this PR has some consensus breaking changes, I added the corresponding breaking:: labels
  • This will require 2 reviewers to approve the changes
  • N/A - documentation change only
• If this PR requires changes to the docs or specs, a corresponding PR is opened in the namada-docs repo
  • Relevant PR if applies: N/A - README.md change only
• If this PR affects services such as namada-indexer or namada-masp-indexer, a corresponding PR is opened in that repo
  • Relevant PR if applies: N/A - README.md change only

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.89%. Comparing base (7a0770d) to head (1746ec4).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4007   +/-   ##
=======================================
  Coverage   73.89%   73.89%           
=======================================
  Files         341      341           
  Lines      106451   106451           
=======================================
+ Hits        78657    78667   +10     
+ Misses      27794    27784   -10     

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