docs: compare with standard go/version

[Rayan-and-beyond]

Closes #153

Adds a short README section explaining when the Go 1.22 go/version package is sufficient and when this library’s broader SemVer parsing and constraint APIs are useful.

Validation:

• checked the documented stdlib operations against the current go/version package docs
• checked the referenced go-version capabilities against the current exported API
• git diff --check

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[tgross]

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