Expand EXDC definition

src/include/Configuration.h

@@ -199,7 +199,7 @@ protected:
 	int number_of_scales;
 	//! \brief Type of dielectric functions (<0 at XIP, =0 as function of XI, >0 contants).
 	int idfc;
-	//! \brief EXDC. QUESTION: better definition?
+	//! \brief External medium dielectric constant. QUESTION: correct?
 	double exdc;
 	//! \brief WP. QUESTION: better definition?
 	double wp;