Add optimized pictures

Included is a script with the optimization commands I ran. Values are
pretty arbitrary; I didn't do much testing after validating that
everything looked good enough.

Fixes #1
Fixes #3

pictures/optimize.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env nix-shell
+#! nix-shell -i bash --pure
+#! nix-shell -p imagemagick
+
+for picture in original/*png; do
+    magick $picture -resize 800x800 -quality 80 $(basename $picture .png)-sm.jpg
+    magick $picture -quality 90 $(basename $picture .png).jpg
+done
+
+for picture in original/*jpg; do
+    magick $picture -resize 800x800 -quality 80 $(basename $picture .jpg)-sm.jpg
+    cp $picture $(basename $picture)
+done