Update cluster size guidelines in docs

(cherry picked from commit c7697e7)

Author: deliahu

docs/clusters/management/create.md

@@ -93,7 +93,7 @@ iam_policy_arns: ["arn:aws:iam::aws:policy/AmazonS3FullAccess"]
 # primary CIDR block for the cluster's VPC
 vpc_cidr: 192.168.0.0/16
 
-# instance type for prometheus (use a larger instance for clusters exceeding 500 nodes)
+# instance type for prometheus (use an instance with more memory for clusters exceeding 300 nodes or 300 pods)
 prometheus_instance_type: "t3.medium"
 ```
 

docs/clusters/management/production.md

@@ -66,7 +66,7 @@ node_groups:
 
 ### Considerations for large clusters
 
-If you plan on scaling your Cortex cluster past 400 nodes or 800 pods, it is recommended to set `prometheus_instance_type` to a larger instance type. A good guideline is that a t3.medium instance can reliably handle 400 nodes and 800 pods.
+If you plan on scaling your Cortex cluster past 300 nodes or 300 pods, it is recommended to set `prometheus_instance_type` to an instance type with more memory (the default is `t3.medium`, which has 4gb).
 
 ## API Spec