Added Comparison Summary mardown

docs/ComparisonSummary.md

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+# Comparison Benchmark Summary
+
+![Operation Rate Comparison](https://storage.googleapis.com/deephaven-benchmark/compare/benchmark-summary.svg?)
+
+## Comparison Table Organization
+
+- Each row shows the benchmark in rows per sec for equivalent operations
+- The versions displayed show the latest stable release of each product
+- The Benchmark Date shows the day when the benchmarks where collected
+
+## Basic Benchmark Methodology
+
+- All products are run on the same hardware in the same environment
+- For each operation (row), all products use the same single parquet file
+- All products are benchmarked "out of the box" with no tuning
+- Parquet read is included in the benchmark
+   - Some products group or index on parquet read
+- Deephaven runs as a service while the other products run in-process
+