Create documentation to explain the service

[agstephens]

1. Create user-facing documentation

Some thoughts:

1. All curated data sets in the CEDA Archive (such as CMIP6, UKCP18, MIDAS-Open, HadUK-Grid, Sentinel) - are accessible read-only from the JASMIN Notebook Service.

2. Group Workspaces are also read-only from the JASMIN Notebook Service. These hold non-curated data sets, such as those brought to JASMIN specifically for a hackathon.

3. Each user has a 100GB HOME directory - so outputs can be written to them.

NOTE: If a user would need to generate >100GB of output then this approach would not work.

2. Create internal documentation