Add documentation for read-only root filesystem

[vepatel]

Proposed changes

• Add docs for read-only root filesystem under "Security"

Checklist

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

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[brianehlert]

editorial and need better exposure for end comments and note

[codecov]

Codecov Report

Merging #3661 (2202a5b) into main (04fe202) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #3661   +/-   ##
=======================================
  Coverage   52.31%   52.31%           
=======================================
  Files          59       59           
  Lines       16853    16853           
=======================================
  Hits         8817     8817           
  Misses       7741     7741           
  Partials      295      295           

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[ciarams87]

👍🏼