Add benchmark results

[mihaibudiu]

We have to choose

• [ ] a set of benchmarks to run
• [ ] a set of systems to compare against Nexmark are a logical choice since we already have them, and we could use them to compare against Flink and RisingWave. But we should find more databasey benchmarks too. I will look at related work more closely. Other systems we can consider: Arryo, Snowflake, Postgres, https://github.com/sraoss/pg_ivm, DBToaster, Databricks

[mihaibudiu]

Maybe we'll do more for the camera-ready