Improve discoverability copy & Maven metadata (#220)

[AndreasIgel]

Summary

Improves how Simple Builders presents itself so it's easier to find and understand when searching for a Java builder library — the file-only subset of #220. Repo settings (GitHub description/topics/social image) and the homepage decision (#221) are intentionally out of scope here.

README

• New keyword-led H1 and a one-line tagline that names the differentiators (records, Jackson, copy-with, conditional, collection helpers; positioned as a lightweight Lombok / RecordBuilder alternative).
• Broadened the "What is Simple Builders?" intro to mention records, Jackson, immutable copy-with, conditional logic, and "no runtime reflection".
• Added a fair, terse Comparison table vs Lombok, Immutables, AutoValue, FreeBuilder, RecordBuilder (captures competitor search intent; the key Simple Builders angle is: works on plain classes and records, standard compile-time annotation processing, minimal runtime deps).

POM metadata (indexed by Maven Central search)

• Fixed the parent pom.xml <description> (was a typo'd, inaccurate "…in maven generate-sources phase"; it's a compile-time annotation processor).
• Tightened core and processor module <description>s for accuracy and keywords.

Out of scope (tracked elsewhere)

• GitHub repository description / topics / social-preview image — settings, not files (checklist in Improve discoverability & positioning (README, POM metadata, GitHub topics/description, SEO) #220).
• Homepage field + Javadoc-vs-docs-site decision — Set a project homepage — decide content (Javadoc site vs docs/landing page) #221.

Relates to #220.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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