misc: Document placeholders

README.md

@@ -1,2 +1,32 @@
 # Chunky-Expansion
 Chunky Expansion for MiniPlaceholders
+
+## Placeholders
+
+```
+<chunky_task_pregen_exists:<world>>
+<chunky_task_pregen_running:<world>>
+<chunky_task_pregen_cancelled:<world>>
+<chunky_task_pregen_centerx:<world>>
+<chunky_task_pregen_centerz:<world>>
+<chunky_task_pregen_radiusz:<world>>
+
+<chunky_task_pregen_radiusx:<world>>
+<chunky_task_pregen_radius:<world>>
+
+<chunky_task_pregen_count:<world>>
+<chunky_task_pregen_pattern:<world>>
+<chunky_task_pregen_shape:<world>>
+<chunky_task_pregen_time:<world>>
+<chunky_task_pregen_world:<world>>
+<chunky_task_pregen_chunks:<world>>
+<chunky_task_pregen_complete:<world>>
+<chunky_task_pregen_percent:<world>>
+<chunky_task_pregen_hours:<world>>
+<chunky_task_pregen_minutes:<world>>
+<chunky_task_pregen_seconds:<world>>
+<chunky_task_pregen_rate:<world>>
+<chunky_task_pregen_x:<world>>
+<chunky_task_pregen_z:<world>>
+
+```