feat: Adds extension to argument parser's command configuration

Sources/CliDoc/Nodes/Abstract.swift

@@ -0,0 +1,14 @@
+import CliDocCore
+
+public struct Abstract<Content: TextNode>: TextNode {
+  @usableFromInline
+  let content: Content
+
+  public init(@TextBuilder content: () -> Content) {
+    self.content = content()
+  }
+
+  public var body: some TextNode {
+    content
+  }
+}

Sources/CliDoc/Nodes/Discussion.swift

@@ -0,0 +1,14 @@
+import CliDocCore
+
+public struct Discussion<Content: TextNode>: TextNode {
+  @usableFromInline
+  let content: Content
+
+  public init(@TextBuilder content: () -> Content) {
+    self.content = content()
+  }
+
+  public var body: some TextNode {
+    content
+  }
+}

Sources/CliDoc/Nodes/Note.swift

@@ -1,6 +1,7 @@
 import CliDocCore
 import Rainbow
 
+// TODO: Use labeled content.
 public struct Note<Label: TextNode, Content: TextNode>: TextNode {
   @usableFromInline
   let label: Label

Sources/CliDoc/Nodes/Usage.swift

@@ -0,0 +1,14 @@
+import CliDocCore
+
+public struct Usage<Content: TextNode>: TextNode {
+  @usableFromInline
+  let content: Content
+
+  public init(@TextBuilder content: () -> Content) {
+    self.content = content()
+  }
+
+  public var body: some TextNode {
+    content
+  }
+}