docs: make intro page follow Robert Ramey's guidelines

[akrzemi1]

This changes the intro page in the docs to be very short and up to the point. Following Robert Ramey's guidelines, the purpose of this page is to convince the user that sees this library for the first time, in ~1 minute that it is wort spending next ~15 minutes reading the overview of this library.

[cppalliance-bot]

An automated preview of the documentation is available at https://397.capy.prtest3.cppalliance.org/index.html

If more commits are pushed to the pull request, the docs will rebuild at the same URL.

2026-09-06 15:39:52 UTC

[cppalliance-bot]

GCOVR code coverage report https://397.capy.prtest3.cppalliance.org/gcovr/index.html
LCOV code coverage report https://397.capy.prtest3.cppalliance.org/genhtml/index.html
Coverage Diff Report https://397.capy.prtest3.cppalliance.org/diff-report/index.html

Build time: 2026-09-06 15:52:08 UTC

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.09%. Comparing base (9dcd6b7) to head (2afe6c1).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #397   +/-   ##
========================================
  Coverage    98.09%   98.09%           
========================================
  Files          130      130           
  Lines         6289     6289           
========================================
  Hits          6169     6169           
  Misses         120      120           

Flag	Coverage Δ
linux	98.08% <ø> (ø)

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