added user docs

docs/conf.py

docs/img/openBIS.png

docs/index.rst

docs/requirements.txt

docs/user-documentation/advance-features/index.rst

...ns-documentation/associate-file-types-to-dataset-types.md

...sers/admins-documentation/create-templates-for-objects.md

...mentation/customise-inventory-of-materials-and-samples.md

.../admins-documentation/customise-inventory-of-protocols.md

...ustomise-parents-and-children-sections-in-object-forms.md

...min-users/admins-documentation/customise-the-main-menu.md

...s/admins-documentation/database-navigation-in-admin-ui.md

...ns-documentation/enable-archiving-to-long-term-storage.md

...neral-admin-users/admins-documentation/enable-barcodes.md

...ins-documentation/enable-transfer-to-data-repositories.md

...eral-admin-users/admins-documentation/history-overview.md

...s/admins-documentation/img/Barcode-generator-1024x466.png

...mins-documentation/img/Excel-import-admin-UI-1024x634.png

...tation/img/Screenshot-2020-02-26-at-10.11.14-1024x708.png

...tation/img/Screenshot-2020-02-26-at-10.24.58-1024x338.png