fix: correct argument order in list.insert example in method-calls documentation

The example code snippet for method call syntax previously showed `list.insert("item", 3)` which incorrectly placed the value before the index. Updated to `list.insert(3, "item")` to match Wren's actual List.insert method signature where the index parameter comes first.

doc/site/method-calls.markdown

@@ -11,7 +11,7 @@ You have a *receiver* expression (here `System`) followed by a `.`, then a name
 are separated by commas:
 
     :::wren
-    list.insert("item", 3)
+    list.insert(3, "item")
 
 The argument list can also be empty: