indicate in docs that summaries should be self-contained

[jmcmichael]

Some summaries currently contain references to specific tables, figures in the supporting evidence. Given that these summaries may be exported to knowledgebases and other contexts that are not required include links/references to supporting evidence, it may not be possible for readers of these isolated summaries to locate the references indicated by the curator.

Therefore, the docs need to be updated to include language encouraging curators to strive to write summaries that are completely self-contained, that do not require readers to refer to external resources to support statements in the summary.