Add README.md to every directory

Each subdirectory now has a README with:
- File inventory table
- Usage guidelines and specifications
- Technical details (viewbox, colors, sizes)
- Cross-references to related assets

icons/social-media/README.md

@@ -0,0 +1,13 @@
+# Social Media Icons
+
+Profile and avatar images sized for social media platforms. Use the K monomark on blue background for square crops, or the circular favicon/colormark for circular crops.
+
+Currently empty. Generate from `../favicon/keylink-favicon.png` or `../../logos/monomark/` assets at these recommended sizes:
+
+| Platform    | Size      |
+|-------------|-----------|
+| Facebook    | 170x170   |
+| LinkedIn    | 400x400   |
+| X / Twitter | 400x400   |
+| Instagram   | 320x320   |
+| Google      | 250x250   |