Document TargetType and LibraryType enum cases

Author: ElektrojungeAtWork

Sources/PackageDescription4/Product.swift

@@ -97,7 +97,9 @@ public class Product: Encodable {
 
         /// The different types of a library product.
         public enum LibraryType: String, Encodable {
+            /// A statically linked library.
             case `static`
+            /// A dynamically linked library.
             case `dynamic`
         }
 

Sources/PackageDescription4/Target.swift

@@ -18,8 +18,11 @@ public final class Target {
 
     /// The different types of a target.
     public enum TargetType: String, Encodable {
+        /// A regular target.
         case regular
+        /// A test target.
         case test
+        /// A system framework target.
         case system
     }