docs: wrote Doxygen comments for all files

refs: #4118

Change-Id: Ib0e7f1926cdabcca5aa401b59b24519412a099f7
diff --git a/src/common.hpp b/src/common.hpp
index 470d8b1..0d67efc 100644
--- a/src/common.hpp
+++ b/src/common.hpp
@@ -19,6 +19,11 @@
  *
  **/
 
+/*! \file
+ * Shared include file to provide a single point-of-entry, and
+ * hopefully improve compile times.
+ */
+
 #ifndef NLSR_COMMON_HPP
 #define NLSR_COMMON_HPP