docs: convert to archive style

[f3l1x]

Summary

• Fixed license badge to use correct repository path (contributte/thumbator instead of minetro/thumbator)
• Fixed grammar: "was maintain" → "was maintained"
• Fixed grammar: "for being used" → "for using"

Changes

The README was already in archive style format following the template, but had a few minor issues that needed correction:

1. License badge was pointing to the old minetro organization instead of contributte
2. Grammar corrections in the Development section

The repository follows Option A of the archive template (with replacement package pointing to contributte/image-storage).

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