docs(Accessibility): improve introduction section

[jurokapsiar]

This PR improves introduction section to accessibility, mainly summarizing what needs to be done in preparation for correct component usage to achieve accessible experiences

[codecov]

Codecov Report

Merging #1368 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1368      +/-   ##
==========================================
- Coverage   72.35%   72.35%   -0.01%     
==========================================
  Files         772      772              
  Lines        5752     5751       -1     
  Branches     1680     1703      +23     
==========================================
- Hits         4162     4161       -1     
  Misses       1584     1584              
  Partials        6        6

Impacted Files	Coverage Δ
packages/react/src/components/Popup/Popup.tsx	68.29% <0%> (-0.2%)	⬇️

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[codecov]

Codecov Report

Merging #1368 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1368      +/-   ##
==========================================
- Coverage   72.35%   72.35%   -0.01%     
==========================================
  Files         772      772              
  Lines        5752     5751       -1     
  Branches     1680     1703      +23     
==========================================
- Hits         4162     4161       -1     
  Misses       1584     1584              
  Partials        6        6

Impacted Files	Coverage Δ
packages/react/src/components/Popup/Popup.tsx	68.29% <0%> (-0.2%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 696c8b9...f092b8c. Read the comment docs.

[codecov]

Codecov Report

Merging #1368 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1368   +/-   ##
=======================================
  Coverage   72.99%   72.99%           
=======================================
  Files         776      776           
  Lines        5828     5828           
  Branches     1726     1706   -20     
=======================================
  Hits         4254     4254           
  Misses       1568     1568           
  Partials        6        6

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 649377a...eab6232. Read the comment docs.