Added alt-tag to CC0-files.

bench/seismic/wp/hsp2a/meshes/CC0.rst

 .. image:: http://i.creativecommons.org/p/zero/1.0/88x31.png
+   :alt: CC0
    :target: http://creativecommons.org/publicdomain/zero/1.0/
 
 To the extent possible under law, `Alexander Nikolas Breuer <https://dial3343.org/>`_ has waived all copyright and related or neighboring rights to the following work:

bench/seismic/wp/hsp2a/sources/CC0.rst

 .. image:: http://i.creativecommons.org/p/zero/1.0/88x31.png
+   :alt: CC0
    :target: http://creativecommons.org/publicdomain/zero/1.0/
 
 To the extent possible under law, `Alexander Nikolas Breuer <https://dial3343.org/>`_ has waived all copyright and related or neighboring rights to the following work:

bench/seismic/wp/loh3/meshes/CC0.rst

 .. image:: http://i.creativecommons.org/p/zero/1.0/88x31.png
+   :alt: CC0
    :target: http://creativecommons.org/publicdomain/zero/1.0/
 
 To the extent possible under law, `Alexander Nikolas Breuer <https://dial3343.org/>`_ has waived all copyright and related or neighboring rights to the following work:

bench/seismic/wp/loh3/sources/CC0.rst

 .. image:: http://i.creativecommons.org/p/zero/1.0/88x31.png
+   :alt: CC0
    :target: http://creativecommons.org/publicdomain/zero/1.0/
 
 To the extent possible under law, `Alexander Nikolas Breuer <https://dial3343.org/>`_ has waived all copyright and related or neighboring rights to the following work: