export readme cleanup

Author: Xor-el

assets/branding/export/README.md

@@ -5,9 +5,9 @@ PNG files in this folder are **generated from** `../logo.svg`.
 | File | Size | Typical use |
 |------|------|-------------|
 | `og-1280x640.png` | 1280×640 | **GitHub social preview** (recommended; 2:1) |
-| `og-640x320.png` | 640×320 | GitHub social preview **minimum** (2:1) |
-| `og-1200x630.png` | 1200×630 | Open Graph / link previews |
+| `og-640x320.png` | 640×320 | GitHub social preview **minimum** size (2:1) |
+| `og-1200x630.png` | 1200×630 | Open Graph / general link previews |
 | `social-header-1500x500.png` | 1500×500 | Twitter/X-style header |
 | `logo-512.png` | 512×512 | Profile / square avatar |
 
-Regenerate after SVG changes (see `../README.md`).
+Regenerate after SVG changes using Inkscape or ImageMagick.