Update documentation about single-line documentation

doc/DOCUMENTATION.md

@@ -23,8 +23,7 @@ map :: (a -> b) [a] -> [b]
 
 For short documentation items, doclines, starting with `//*` can be used. When
 documenting a constructor, or record field, they should be placed *after* the
-item they document. Doclines are only supported for constructors and record
-fields. For example:
+item they document. For example:
 
 ```clean
 /**
@@ -37,6 +36,23 @@ fields. For example:
 	}
 ```
 
+To add several lines of documentation to a constructor or record field, several
+doclines can be used:
+
+```clean
+:: MyType
+	= MyConstructor args // ...
+		//* This constructor may require some more explanation,
+		//* which is added on several lines.
+```
+
+Doclines can also be added *above* a function, type, or class definition:
+
+```clean
+//* The identity function.
+id :: .a -> .a
+```
+
 ## Markup in documentation
 
 Some simple Markdown-inspired markup is allowed in documentation: