Add convenience box command

Sources/Generator/Templates/Elements/BoxTemplate.swift

@@ -1,13 +1,13 @@
 import Foundation
 
-struct PlaceholderTemplate: Template {
+struct BoxTemplate: Template {
 
     enum Key: String, CaseIterable {
         case title = "TITLE"
         case text = "TEXT"
     }
 
-    static let templateName = "empty.html"
+    static let templateName = "box.html"
 
     var raw: String
 }