docs: improve README with detailed usage and installation instructions

[kazeburo]

PR Type

Documentation

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Description

• Expands README with Japanese usage guidance

• Documents installation and agent configuration

• Explains metrics, categories, and daemon architecture

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Diagram Walkthrough

flowchart LR
  README["Expanded README"] -- "documents installation" --> Installation["Installation methods"]
  README -- "explains configuration" --> Configuration["Mackerel agent setup"]
  README -- "describes outputs" --> Metrics["Metrics and categories"]
  README -- "documents internals" --> Architecture["Daemon architecture"]

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File Walkthrough

	Relevant files
Documentation	README.md Expand README installation and operational guidance            README.md Rewrites the introduction in Japanese with a clearer plugin overview. Adds installation instructions for mkr and release binaries. Documents command usage, agent configuration, metrics, categories, and meanings. Explains daemon behavior, CPU statistics collection, history retention, and licensing. +133/-15

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[github-actions]

PR Reviewer Guide 🔍

(Review updated until commit b51452e)

Here are some key observations to aid the review process:

⏱️ Estimated effort to review: 1 🔵⚪⚪⚪⚪

🧪 No relevant tests

🔒 No security concerns identified

⚡ No major issues detected

[github-actions]

Persistent review updated to latest commit fa79d7b

[github-actions]

PR Code Suggestions ✨

No code suggestions found for the PR.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Persistent review updated to latest commit b51452e