DOC: Add quick start

[pllim]

Description

This PR adds a quick start section for lazy people like me. Would have helped when I don't care about running the pipeline but just wants to know quickly how to read your product.

Checklist

• [x] Tests -- N/A
• [x] Documentation
• [x] Change log -- N/A
• [ ] Milestone -- I cannot add this, so you have to
• [ ] Label(s) -- I cannot add this, so you have to. Do you know that Action can auto-add labels?

[pllim]

Example to load both to astropy.nddata.CCDData is even better, but when I tried with astropy 4.3.dev, CCDData does not understand GWCS; alas!

[codecov[bot]]

Codecov Report

Merging #5976 (c024f49) into master (d26b6f0) will not change coverage. The diff coverage is n/a.

:exclamation: Current head c024f49 differs from pull request most recent head 627be55. Consider uploading reports for the commit 627be55 to get more accurate results

@@           Coverage Diff           @@
##           master    #5976   +/-   ##
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  Coverage   77.77%   77.77%           
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  Files         404      404           
  Lines       35367    35367           
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  Hits        27505    27505           
  Misses       7862     7862           

Flag	Coverage Δ		*Carryforward flag
nightly	77.77% <ø> (ø)		Carriedforward from d26b6f0
unit	56.20% <ø> (ø)

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[pllim]

Rendered doc: https://jwst-pipeline--5976.org.readthedocs.build/en/5976/jwst/data_products/quickstart.html

[nden]

I am going to close this one because the documentation has been reworked.