tweaks to README, security notes, contributing guide, PR template

[fabriciojs]

Issue	#248
🪲 Bug Fix	No
🏆 Feature	No
📝 Refactor	No
📖 Documentation	Yes
⚠️ Break Change	No

Description

• Simplifying and reducing a lot the PR template
• Creating CONTRIBUTING.md
• Removing old demo video, linking to ASCII Cinema page
• Fix outdated security notes on supporting versions

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Notes

How it will look like for the developer opening the PR:

[codecov]

Codecov Report

Merging #249 (bca0438) into master (4d7176e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #249   +/-   ##
=======================================
  Coverage   88.03%   88.03%           
=======================================
  Files          66       66           
  Lines        2565     2565           
=======================================
  Hits         2258     2258           
  Misses        283      283           
  Partials       24       24           

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