Add 26.3 descriptive book binding and travel

ports/mc263/README.md

@@ -3,8 +3,10 @@
 This is an **experimental alpha port** for issues #97–#104, not gameplay parity
 with the Minecraft 1.21.1 release. It registers basic items and a runtime Age
 prototype with persisted seeds. The operator-only `rivencraft_port age`
-commands create and inspect separate vanilla-terrain levels. Descriptive Book
-travel and named Linking Book binding/travel work as limited probes. Authored
+commands create and inspect separate vanilla-terrain levels. The current
+development slice can name an unbound Descriptive Book to create a prototype
+Age, then enter it from the book GUI; the player verified this interaction in game.
+Named Linking Book binding/travel works as a limited probe. Authored
 generation, most content, recipes, workstations, portal systems, modifiers and
 the destination preview renderer remain unported. Use a test world and keep a
 backup; do not substitute this JAR for the 1.21.1 mod or import 1.21.1 saves.