Merge branch 'preview' into 'add-contrib-guide-for-browser-users'

Dockerfile

README.md

contribute_container.md

doc.zih.tu-dresden.de/README.md

doc.zih.tu-dresden.de/docs/access/jupyterhub.md

doc.zih.tu-dresden.de/docs/access/jupyterhub_for_teaching.md

doc.zih.tu-dresden.de/docs/access/security_restrictions.md

doc.zih.tu-dresden.de/docs/access/ssh_login.md

doc.zih.tu-dresden.de/docs/application/misc/add_member.png

...ih.tu-dresden.de/docs/application/misc/external_login.png

doc.zih.tu-dresden.de/docs/application/misc/members.png

doc.zih.tu-dresden.de/docs/application/misc/overview.png

doc.zih.tu-dresden.de/docs/application/misc/password.png

...h.tu-dresden.de/docs/application/misc/project_details.png

...h.tu-dresden.de/docs/application/misc/request_step1_b.png

...resden.de/docs/application/misc/request_step2_details.png

...esden.de/docs/application/misc/request_step3_machines.png

...esden.de/docs/application/misc/request_step4_software.png

...en.de/docs/application/misc/request_step5_description.png

...zih.tu-dresden.de/docs/application/misc/request_step6.png