feat: Add module diagram in ROADMAP.md

Author: PaulJPhilp

ROADMAP.md

@@ -0,0 +1,26 @@
+graph TD
+    subgraph "Step 2: Build Your Applications"
+        A7["<strong>Layer 7: Your Application</strong><br/>(The final product you build)"]
+        A6["<strong>Layer 6: Application SDKs</strong><br/>(Effect/AI, Effect/cli)"]
+        A5["<strong>Layer 5: The Platform</strong><br/>(@effect/platform)"]
+    end
+
+    subgraph "Step 1: Build Your Services"
+        subgraph "Layer 4: Service Architecture"
+            B4["<strong>4b: Distributed Services</strong><br/>@effect/cluster, @effect/rpc, @effect/workflow"]
+            A4["<strong>4a: Services</strong><br/>Layer, Service, Context"]
+        end
+        A3["<strong>Layer 3: Tools for Services</strong><br/>Stream, Schedule, Schema, Data, etc."]
+        A2["<strong>Layer 2: Runtime</strong><br/>Runtime, Fiber"]
+        A1["<strong>Layer 1: Effect</strong><br/>The Core Blueprint"]
+    end
+
+    %% --- The Flow ---
+    A7 --> A6
+    A6 --> A5
+    A5 --> A4
+    A5 --> B4
+    A4 --> A3
+    B4 --> A3
+    A3 --> A2
+    A2 --> A1