Add builder method to struct in builder pattern (#251)

patterns/creational/builder.md

@@ -13,6 +13,14 @@ pub struct Foo {
     bar: String,
 }
 
+impl Foo {
+    // This method will help users to discover the builder
+    pub fn builder() -> FooBuilder {
+        FooBuilder::default()
+    }
+}
+
+#[derive(Default)]
 pub struct FooBuilder {
     // Probably lots of optional fields.
     bar: String,
@@ -103,6 +111,6 @@ as well as the `FooBuilder::new().a().b().build()` style.
 - [Description in the style guide](https://web.archive.org/web/20210104103100/https://doc.rust-lang.org/1.12.0/style/ownership/builders.html)
 - [derive_builder](https://crates.io/crates/derive_builder), a crate for automatically
   implementing this pattern while avoiding the boilerplate.
-- [Constructor pattern](../idioms/ctor.md) for when construction is simpler.
+- [Constructor pattern](../../idioms/ctor.md) for when construction is simpler.
 - [Builder pattern (wikipedia)](https://en.wikipedia.org/wiki/Builder_pattern)
 - [Construction of complex values](https://web.archive.org/web/20210104103000/https://rust-lang.github.io/api-guidelines/type-safety.html#c-builder)