Add section about LDoc in the contributing guide.

docs/02-contributing.md

@@ -40,6 +40,39 @@ Imitate the existing code style. For concrete rules:
 
 A vim modeline is set in each file to respect this.
 
+### Documentation of lua files
+
+For documentation purposes LDoc---see
+[here](https://stevedonovan.github.io/ldoc/manual/doc.md.html) for its
+documentation---is used. Comments, that shall be parsed by LDoc have the following format:
+
+    --- summary.
+    -- Description; this can extend over
+    -- several lines
+    
+    -----------------
+    -- This will also do.
+    
+    --[[--
+     Summary. A description
+     ...;
+    ]]
+
+One can use the full power of [Markdown](http://daringfireball.net/projects/markdown)
+with the extensions of [Discount](http://www.pell.portland.or.us/~orc/Code/discount/)
+for mark-up in the comments.
+
+Every module and class should have a short description at its beginning which
+should include `@author author`, `@copyright year author`,
+`@release @AWESOME_VERSION@` and `@module module-name` or `@classmod class-name`.
+Parameters of functions should be documented by `@param parameter description`,
+return values via `@return description` or `@treturn type description`. For a
+more comprehensive description of the available tags see the
+[LDoc documentation](https://stevedonovan.github.io/ldoc/manual/doc.md.html).
+
+In addition to the regular tags provided by LDoc there are also some aliases for
+tags defined in `docs/config.ld`.
+
 ## Patches
 
 If you plan to submit patches, you should follow the following guidelines.