Documented the AppArguments protocol and the Environment+Properties extension in the library target.

Test/Sources/Helpers/TestArguments.swift

@@ -2,11 +2,11 @@ import AppLibrary
 import Logging
 
 struct TestArguments: AppArguments {
-
+    
     // MARK: Properties
-
+    
     let hostname = "127.0.0.1"
-    let port = 0
     let logLevel: Logger.Level? = .trace
-
+    let port = 0
+    
 }