Add a guide for loading in data

[d47853]

A common need will be for users to load in their own data. Add a guide detailing how to do this including:

• Loading via REST
• Loading via HDFS
• Loading via accumulo import

The guide should cover how to do this on Kubernetes, as well as locally (using docker compose)

[GCHQDeveloper314]

This doc should form part of the gaffer-doc repo. See #24