HPCC-9083 Document ECLWatch Tech Preview

Fix HPCC-9083 Document ECLWatch Tech Preview
Documenting changes to ECLWatch for Technical
Preview (for upcoming interface changes in 4.0)

Signed-off-by: g-pan <greg.panagiotatos@lexisnexis.com>
Merge pull request #4231 from g-pan/H9083-TechPreView

HPCC-9083 Document ECLWatch Tech Preview

Reviewed-By: Gordon Smith <gordon.smith@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>