Update performance guide

Author: szarnyasg

docs/preview/guides/performance/my_workload_is_slow.md

@@ -5,7 +5,7 @@ title: My Workload Is Slow
 
 If you find that your workload in DuckDB is slow, we recommend performing the following checks. More detailed instructions are linked for each point.
 
-1. Do you have enough memory? DuckDB works best if you have [5-10 GB memory per CPU core]({% link docs/preview/guides/performance/environment.md %}#cpu-and-memory).
+1. Do you have enough memory? DuckDB works best if you have [1-4 GB memory per thread]({% link docs/preview/guides/performance/environment.md %}#cpu-and-memory).
 1. Are you using a fast disk? Network-attached disks (such as cloud block storage) cause write-intensive and [larger than memory]({% link docs/preview/guides/performance/how_to_tune_workloads.md %}#spilling-to-disk) workloads to slow down. For running such workloads in cloud environments, it is recommended to use instance-attached storage (NVMe SSDs).
 1. Are you using indexes or constraints (primary key, unique, etc.)? If possible, try [disabling them]({% link docs/preview/guides/performance/schema.md %}#indexing), which boosts load and update performance.
 1. Are you using the correct types? For example, [use `TIMESTAMP` to encode datetime values]({% link docs/preview/guides/performance/schema.md %}#types).