feat: Working on node builder

Sources/CliDoc/Node.swift

@@ -0,0 +1,26 @@
+// swiftlint:disable type_name
+public protocol Node: NodeRepresentable {
+  associatedtype _Body: NodeRepresentable
+  typealias Body = _Body
+
+  @NodeBuilder
+  var body: Body { get }
+}
+
+// swiftlint:enable type_name
+
+public extension Node {
+  @inlinable
+  func render() -> String {
+    body.render()
+  }
+}
+
+public struct Foo: Node {
+
+  public init() {}
+
+  public var body: some NodeRepresentable {
+    LabeledContent("Foo") { "Bar" }
+  }
+}