new_node: Documented rr_data structure in node.h.

src/knot/zone/node.h

@@ -91,10 +91,11 @@ struct knot_node {
 
 typedef struct knot_node knot_node_t;
 
+/*!< \brief Structure storing RR data. */
 struct rr_data {
-	uint16_t type;
-	knot_rrs_t rrs;
-	knot_node_t **additional;
+	uint16_t type; /*!< \brief RR type of data. */
+	knot_rrs_t rrs; /*!< \brief Data of given type. */
+	knot_node_t **additional; /*!< \brief Additional nodes with glues. */
 };
 
 /*----------------------------------------------------------------------------*/