Creating Tutorials section and moving Video Tutorial there

web/content/docs/tutorials/_index.md

web/content/docs/tutorials/video-tutorial/OGSinput_basin.prj

web/content/docs/tutorials/video-tutorial/_index.md

web/content/docs/tutorials/video-tutorial/glacierclass.py

web/content/docs/tutorials/video-tutorial/history.sh

web/content/docs/tutorials/video-tutorial/mesh_basin.msh

web/content/docs/tutorials/video-tutorial/mesh_basin.py

web/content/docs/tutorials/video-tutorial/timeBCs_glacier.py

...ocs/tutorials/video-tutorial/video_tutorial_thumbnail.png