README: add sixel/kitty links

README.md

@@ -269,6 +269,7 @@ to breaking under incorrect `TERM` values. If you're not using `xterm`, your
 * [UTF-8 Decoder Capability and Stress Test](https://www.cl.cam.ac.uk/~mgk25/ucs/examples/UTF-8-test.txt)
 * [Emoji: how do you get from U+1F355 to 🍕?](https://meowni.ca/posts/emoji-emoji-emoji/)
 * [Glyph Hell: An introduction to glyphs, as used and defined in the FreeType engine](http://chanae.walon.org/pub/ttf/ttf_glyphs.htm)
+* My wiki's [Sixel page](https://nick-black.com/dankwiki/index.php?title=Sixel) and Kitty's [extensions](https://sw.kovidgoyal.net/kitty/protocol-extensions.html).
 
 ### Useful man pages
 * Linux: [console_codes(4)](http://man7.org/linux/man-pages/man4/console_codes.4.html)