docs: fix spelling, formatting, and accuracy issues in README

[kranthipoturaju]

Improves the README to production quality by addressing spelling, grammar, formatting consistency, Markdown syntax, and documentation accuracy.

Changes

Correctness

• Fix Github → GitHub in the document title
• Align configFile default (./commitlint.config.mjs) with action.yml
• Rewrite failOnErrors description, which previously described false
  behavior while the default is true
• Update stale GitHub token docs URL
• Remove trailing commas from the JSON output example (invalid JSON)

Formatting & Markdown

• Remove trailing colon from #### Important Note: heading
• Normalize all default: labels to Default: for consistency
• Change JSON code fence language identifier to lowercase json
• Wrap merge_group and pull_request event names in backticks in prose
• Promote the config file note to bold (**Note:**) and add missing period
• Fix Docker link text (removed spurious backtick inside link label)

Prose

• Replace "env var" with "environment variable"
• Replace "In order to do so, …" with "To do so, …"
• Replace "Apart from" with "In addition to"
• Minor wording improvements throughout

[Copilot]

Pull request overview

This PR updates the repository README to improve documentation correctness and presentation quality for the Commitlint GitHub Action.

Changes:

• Fixes naming/formatting issues (e.g., “GitHub”, headings, Markdown code fences, valid JSON example output).
• Aligns/clarifies several input descriptions and defaults (e.g., configFile, failOnErrors) and improves prose consistency.
• Updates guidance around merge queue usage and related workflow examples.

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

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