docs: update README for v0.3.0

Added "What's New in v0.3" section covering species, concepts,
sub_concepts, concept_comparison, template species inheritance,
and life arc field requirements. Updated quick start example
with v0.3 syntax including species and type system declarations.

examples/baker-family/schema/life_arcs.sb

@@ -0,0 +1,46 @@
+//! Life arc definitions for the Baker family
+//!
+//! Demonstrates v0.3.0 life arc features:
+//! - Field requirements with type annotations (requires clause)
+//! - State transitions with conditions
+
+// Career progression for bakers
+life_arc BakerCareer requires { baking_skill: Number, work_ethic: Number } {
+    state apprentice {
+        on enter {
+            specialty: "learning"
+        }
+        on baking_skill > 0.5 and work_ethic > 0.7 -> journeyman
+    }
+
+    state journeyman {
+        on enter {
+            specialty: "bread"
+        }
+        on baking_skill > 0.8 and work_ethic > 0.9 -> master
+    }
+
+    state master {
+        on enter {
+            specialty: "artisan"
+        }
+    }
+}
+
+// Growth arc for children
+life_arc Childhood requires { age: Number, curiosity: Number } {
+    state young_child {
+        on age > 5 -> school_age
+    }
+
+    state school_age {
+        on age > 12 -> teenager
+    }
+
+    state teenager {
+        on age > 18 -> adult
+    }
+
+    state adult {
+    }
+}