Documentation missing for minimum cloud config requirements

[bodymindarts]

The diego-cell vm types are specified as small-highmem which in autogenerated cloud-config in the lab are defined as:

- {"name": "small-highmem","cloud_properties": {"cpu": 4,"disk": 10240,"ram": 8192}}

Deployment of Diego cells onto those vms will fail due to: https://community.pivotal.io/s/article/Diego-Cell-rep-service-fails-with-message-auto-disk-limit-must-result-in-a-positive-number?language=en_US

cc @ramonskie

[dennisjbell]

Upstream's definition of small-highmem has insufficient disk size for diego cells. This can be resolved by either updating the documentation in MANUAL.md, and/or updating the pre-deploy hook to check the disk size. While it may seem ideal to do the latter, the different IaaS' make the detection of this very difficult, ESPECIALLY Asure (which can reference disk sizes indirectly). It is therefore recommended to provide documentation to capture this problem.

[dennisjbell]

Acceptance Criteria:

Document memory, disk and cpu requirements for instance group types.

[dennisjbell]

This was also the cause of #33, which has been closed and incorporated into this ticket by specifying the expanded title and Acceptance Criteria