Update DataFusion instructions / Enable swap on small machines

[alamb]

• Related to Update Results for DataFusion 52.0.0 #749 / Revert "Update Results for DataFusion 52.0.0" #766
• Related to Update ClickBench benchmarks with DataFusion 52.0.0 apache/datafusion#19826

Rationale

I would like to

1. Get the ClickBench benchmark results reflecting the most recent version of DataFusion
2. More easily run pre-release DataFusion benchmarks in the ClickBench harness so we can evaluate their impact (e.g. Analyze current ClickBench performance with DataFusion 52 apache/datafusion#20601)

Since we last successfully ran the benchmarks ourselves (47.0.0), new smaller machines (c6a.xlarge 4core, 8G RAM) where the existig scripts have struggled a lot. Specifically:

1. rustc is OOM killed (due to the link flags we pass)
2. datafusion-cli is OOM killed (due to issues such as datafusion-cli fails to run ClickBench queries with 8GB of RAM apache/datafusion#18473)

Also, the existing instructions are somewhat outdated

Changes

1. Update README.md to reflect reality, and incorporate changes from @waynexia in Update Results for DataFusion 52.0.0 #749 (reverted by Revert "Update Results for DataFusion 52.0.0" #766)
2. Automatically enable swap on low memory machines (as requested by @rschu1ze in Update Results for DataFusion 52.0.0 #749 (comment))
3. Add in the make-json.sh script to help us evaluate the current status locally

Non Changes

Note this PR does NOT update any results (I will make a follow on PR with actual numbers, I want to get the scripts into shape first)

Testing

I tested on these machines following the instructions

• c6.xlarge
• c8g.4xlarge

[alamb]

FYI @pmcgleenon and @waynexia I wonder what you think of this approach (just turning on swap)?