fix(readme): use absolute URLs for logo images so they render on PyPI

[frivas-at-navteca]

Summary

• Fixes the broken logo image on the PyPI project page
• Replaces relative paths (docs/assets/logo-*.svg) with absolute raw.githubusercontent.com URLs
• PyPI does not serve local files, so relative paths result in a broken image; absolute URLs work both on PyPI and GitHub

Closes #62

Note: AI assisted with identifying the root cause and generating the fix. The change is a straightforward 3-line diff that I understand fully.