docs: update prose about image tag/name format

[dvdksn]

- What I did

Update the verbiage about the format of image tags/names.

• Addresses Docker image tag spec is ambiguous docs#20893

- How I did it

/usr/bin/nvim

- How to verify it

read it

- A picture of a cute animal (not mandatory but encouraged)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.92%. Comparing base (6ed137f) to head (a1ca594).
Report is 12 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5535      +/-   ##
==========================================
+ Coverage   60.67%   60.92%   +0.25%     
==========================================
  Files         345      345              
  Lines       23491    23491              
==========================================
+ Hits        14252    14313      +61     
+ Misses       8266     8205      -61     
  Partials      973      973              

[laurazard]

This looks fantastic! Thanks 🤗