Clarify the "duplicate documentation" remark

This remark is intended for maintainers, not for users. It should not have
been in the Doxygen typeset part.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index 8b781a0..2d2c67a 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -3703,11 +3703,15 @@
  *
  * Our advice is to enable options and change their values here
  * only if you have a good reason and know the consequences.
- *
- * Please check the respective header file for documentation on these
- * parameters (to prevent duplicate documentation).
  * \{
  */
+/* The Doxygen documentation here is used when a user comments out a
+ * setting and runs doxygen themselves. On the other hand, when we typeset
+ * the full documentation including disabled settings, the documentation
+ * in specific modules' header files is used if present. When editing this
+ * file, make sure that each option is documented in exactly one place,
+ * plus optionally a same-line Doxygen comment here if there is a Doxygen
+ * comment in the specific module. */
 
 /* MPI / BIGNUM options */
 //#define MBEDTLS_MPI_WINDOW_SIZE            6 /**< Maximum window size used. */