Add per-pattern README.md for the 5 creational patterns (Factory Method, Abstract Factory, Builder, Prototype, Singleton) for consistency with all other 18 patterns

01-creational/builder/README.md

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+# Builder Design Pattern — Java Example
+
+**Pattern:** Creational → Builder
+**Article:** https://ankurm.com/builder-design-pattern-java/
+
+## What this example shows
+
+An immutable `HttpRequest` assembled step by step instead of through a constructor with a dozen optional parameters. `HttpRequest` is the product — built once, never mutated afterward. `HttpClientConfig` is a director-style helper that encapsulates common request configurations so callers don't repeat the same builder calls. `Main` wires it together and shows the fluent builder chain in action.
+
+## How to run
+
+```bash
+javac builder/*.java -d out/builder
+java -cp out/builder builder.Main
+```
+
+Requires Java 25.
+
+## Post Section ↔ File Mapping
+
+| Post Section | File(s) |
+|---|---|
+| Part 1 — The Product: HttpRequest (Immutable) | `HttpRequest.java` |
+| Part 2 — The Director: Encapsulating Common Configurations | `HttpClientConfig.java` |
+| Part 3 — Using the Builder: Client Code | `Main.java` |
+
+Note: the Lombok `@Builder` example and the JDK standard-library snippets (`HttpRequest.newBuilder()`, `StringBuilder`, `ProcessBuilder`) are illustrative only — they are not part of this repository's runnable example.
+
+Article: https://ankurm.com/builder-design-pattern-java/
+All patterns: https://ankurm.com/design-patterns-java/