Fill the documentation

[Markel]

Adds these new sections to the HOW_TO_WRITE_FEATURE_DETECTS.md:

• Polyfills
• Submitting a PR (simple)
• Testing
• Install the basics (simplistic)
• Multiple rephrases for better readability

It also reorders some files to follow alphabetical order.

[codecov]

Codecov Report

Merging #2561 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2561   +/-   ##
=======================================
  Coverage   95.15%   95.15%           
=======================================
  Files           5        5           
  Lines         165      165           
=======================================
  Hits          157      157           
  Misses          8        8           

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[Markel]

I'll soon solve the conflicts

[Markel]

Okay merge conflicts solved, still there is a broken link link with the Verify/Run your tests (seems that Github Markdown parser doesn't like slashes but the url redirect yes, etc) so I'll probably will change the name in the next commit (I assume that some extra tweaking will be needed).
Also, the install the basics section doesn't end up convincing me :/

[rejas]

lgtm. what do you think @patrickkettner ?

[Markel]

🤔 I was thinking about the testing section, maybe it would be a good idea to put the General testing & Caniuse testing at level 4 under a Create Tests section (level 3) so it is more obvious that those 2 are for creating and different from the verify and running section.

Moreover, the testing section would be duplicated if we merge this PR (check the README)

[rejas]

Since @patrickkettner went dark again, I'd merge it even without his review. Or what do you say @MarkelFe ?

[Markel]

Up to you @rejas

I mean, I think that nothing is technically wrong, so suggestions and improvements (some even mentioned by me) can be added later down the road. But yeah, up to you 🙃