Update container metrics README to link to scraper docs

[dhurley]

Proposed changes

Update container metrics README to link to scraper docs.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• I have run make install-tools and have attached any dependency changes to this pull request
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• If applicable, I have updated any relevant documentation (README.md)
• If applicable, I have tested my cross-platform changes on Ubuntu 22, Redhat 8, SUSE 15 and FreeBSD 13

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.31%. Comparing base (c162d76) to head (6c34341).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1443      +/-   ##
==========================================
+ Coverage   85.18%   85.31%   +0.13%     
==========================================
  Files         102      102              
  Lines       12974    12974              
==========================================
+ Hits        11052    11069      +17     
+ Misses       1437     1418      -19     
- Partials      485      487       +2     

see 6 files with indirect coverage changes

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