docs(readme): polish intro, quickstart, bottom matter, and example consistency

[adrianbrad]

Apply README gaps identified against standard-readme + a review pass over the existing examples.

Top matter

• Replace three-sentence intro with a one-line tagline.
• Add a Features bullet list.
• Surface pkg.go.dev as a prominent body link.

New sections

• Quick start snippet between Import and Choosing a queue.
• Contributing, Security, License at the bottom, each linking to the file already in the repo.
• Maintainer callout.

Per-queue example fixes

• Linked Queue: variable was named circularQueue (copy-paste from Circular) — renamed to linkedQueue.
• Priority Queue: misaligned closing paren; "comparator function" → "less function" (matches code).
• Blocking Queue: switched Println("elem: ", elem) to Printf("elem: %d\n", elem) — Println inserts a space between operands, so the old elem: 2 comment was actually wrong.
• Normalised indentation of all code samples to tabs.

Nits

• Trailing whitespace on a couple of lines.
• Trailing space in the ## Benchmarks heading.
• Removed the awkward "Benchmarks and Example tests can be found…" sentence.
• Quick-start // 1, 2, 3, 4 comment moved above the loop so it doesn't look like the output of a single Println.
• Benchmark-shape sentence now covers Priority and Delay (both zero-alloc post recent changes).

No code changes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (3472c91) to head (01c8a97).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #63   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            6         6           
  Lines          639       639           
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  Hits           639       639           

Flag	Coverage Δ
unittests	100.00% <ø> (ø)

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