Update nextcloud guidance after migration to sequoia

[danielleferraro]

We now have an emLab-only Nextcloud instance that will live on sequoia (migration to occur next week). This will solve group permissions issues that weren't allowing read/write access for folders created in the Nextcloud UI. Once the migration to sequoia is complete, we'll need to update the manual with the new link to Nextcloud (emlab-nextcloud.grit.ucsb.edu) in the guidance here.