chore(docs): XMLBuilder initialIndentationLevel example

Author: moki

docs/v4/3.XMLBuilder.md

@@ -175,6 +175,43 @@ Don't consider attributes while building XML. Other attributes related propertie
 ## indentBy
 Applicable only if `format:true` is set.
 
+## initialIndentationLevel
+Applicable only if `format:true` is set.
+
+Allows you to specify initial indentation level for the builder, with default value being `0`.
+
+Example of setting `initialIndentationLevel` option to custom value and building XML:
+
+```
+const data = {
+    ['trans-unit']: {
+        source: 'source string',
+        target: 'target string',
+    },
+};
+
+const options = {
+    format: true,
+    initialIndentationLevel: 1,
+};
+
+const builder = new XMLBuilder(options);
+const result = builder.build(data);
+
+console.log(result);
+```
+
+Output:
+
+```
+  <trans-unit>
+    <source>source string</source>
+    <target>target string</target>
+  </trans-unit>
+```
+
+Giving us prefixed xml document by one indentation level.
+
 ## preserveOrder
 When you parse a XML using XMLParser with `preserveOrder: true`, the result JS object has different structure. So parse that structure in original XML, you should set the same option while building the XML from that js object.