docu: small remark on docu section in style guide

Author: torbjoernk

doc/source/style_guide.md

@@ -105,9 +105,17 @@ We agreed on using the "most common" C++11 features.  These are:
 
 Document your code.
 
-We use [Doxygen] for generating the documentation webpage.  You can
-use pretty much all the features, Doxygen provides, including
-[MathJAX] for formulas and [Markdown] for easy text formatting.
+We use [Doxygen] for generating the documentation webpage. You can use pretty much all the features,
+Doxygen provides, including [MathJAX] for formulas and [Markdown] for easy text formatting.
+
+It is advised to use Doxygen's special commands wherever possible to aid readability of the 
+generated documentation.
+Especially, one should use `@tparam <T> <description>`, `@param[<in>,<out>] <param> <description>`,
+`@returns <description>`, `@throws <exception> <description>`.
+
+There is an additional custom defined block available to mark documentation of internals.
+Therefore, sourround the respective block with `internals` and `endinternals` (as Doxygen commands).
+
 
 ## Formatting