(Fuser_real_login_name): Doc fix.

src/editfns.c

@@ -493,7 +493,8 @@ that determines the value of this function.")
 DEFUN ("user-real-login-name", Fuser_real_login_name, Suser_real_login_name,
   0, 0, 0,
   "Return the name of the user's real uid, as a string.\n\
-Differs from `user-login-name' when running under `su'.")
+This ignores the environment variables LOGNAME and USER, so it differs from
+`user-login-name' when running under `su'.")
   ()
 {
   return Vuser_real_name;