Merge pull request #64 from tarao/doc-unnamed-construction

Document for unnamed construction

docs/extensible-records.md

@@ -17,6 +17,15 @@ Then use `%` as a constructor to instantiate a record.
 val person = %(name = "tarao", age = 3)
 ```
 
+In addition, you can omit field names when they are the same as variable names.
+
+```scala mdoc:mline
+val name = "tarao"
+val age = 3
+
+%(name, age)
+```
+
 Field Access
 ------------