Update outsource-bottom-up.md

Author: andyblundell

patterns/outsource-bottom-up.md

@@ -26,7 +26,7 @@ Use managed services where available and appropriate. The aim is to reduce opera
 * For data persistence prefer (where there are no other differentiating factors) pay per request options (e.g. Amazon DynamoDB, S3) to pay per time choices (e.g. Amazon Aurora or RDS).
 * In general, prefer solutions which do not involve managing VMs if possible, and ideally where there is no explicit configuration of a network (e.g. subnets, internet gateways, NAT gateways) — compare AWS Lambda which needs no network with AWS Fargate which does.
 * Where possible, outsource the management (including renewal) of certificates (e.g. via [AWS Certificate Manager](https://aws.amazon.com/certificate-manager/))
-  * Where that isn't possible, still prefer outsourcing the management of alerting for certificate expiry
+  * Where that isn't possible, still prefer outsourcing the management of alerting for certificate expiry (see [observability](../practices/observability.md))
 
 ## Cloud native vs cloud agnostic