Create empty markdown files for elements

WebsiteGenerator/Files/FileSystem.swift

@@ -150,9 +150,12 @@ final class FileSystem {
         }
     }
 
-    func contentOfOptionalFile(atPath path: String, source: String) -> String? {
+    func contentOfOptionalFile(atPath path: String, source: String, createEmptyFileIfMissing: Bool = false) -> String? {
         let url = input.appendingPathComponent(path)
         guard exists(url) else {
+            if createEmptyFileIfMissing {
+                try? Data().write(to: url)
+            }
             return nil
         }