[Docs] Update snippets' readme

[peter-csala]

Pull Request

The issue or feature being addressed

Details on the issue fix or feature implementation

• Updated the how to refer to a snippet statement (ref)
• Added a note about referring to non-existing snippet

Confirm the following

• I started this PR by branching from the head of the default branch
• I have targeted the PR to merge into the default branch
• I have included unit tests for the issue/feature
• I have successfully run a local build

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (f617b41) 84.56% compared to head (bf6d15f) 84.56%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1721   +/-   ##
=======================================
  Coverage   84.56%   84.56%           
=======================================
  Files         307      307           
  Lines        6790     6790           
  Branches     1043     1043           
=======================================
  Hits         5742     5742           
  Misses        839      839           
  Partials      209      209           

Flag	Coverage Δ
linux	84.56% <ø> (ø)
macos	84.56% <ø> (ø)
windows	84.56% <ø> (?)

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