Improve deprecation information.

CHANGELOG.md

@@ -43,6 +43,9 @@ SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception
 
 - Removed deprecated `MultyTypeBlockVector::count()`, use `N()` instead.
 
+- Deprecated `writeSVGMatrix` with `std::stream` as the second argument. Use the method
+  with `std::stream` as the first argument.
+
 
 # Release 2.9
 

dune/istl/io.hh

@@ -845,9 +845,12 @@ namespace Dune {
    * @param mat           The matrix to write
    * @param out           A output stream to write SVG to
    * @param opts          SVG Options object
+   *
+   * \deprecated Use signature where std::stream is the first argument. This
+   *             method will be removed after Dune 2.10.
    */
   template <class Mat, class SVGOptions = DefaultSVGMatrixOptions>
-  [[deprecated("Use signature where std::stream is the first argument.")]]
+  [[deprecated("Use signature where std::stream is the first argument. This will be removed after Dune 2.10.")]]
   void writeSVGMatrix(const Mat &mat, std::ostream &out, SVGOptions opts = {}) {
     writeSVGMatrix(out, mat, opts);
   }