Update ch10-app-secrets.md

Author: markjprice

docs/ch10-app-secrets.md

@@ -1,10 +1,14 @@
 **App Secrets**
 
 - [What is an app secret?](#what-is-an-app-secret)
+- [Database connection strings](#database-connection-strings)
 
 # What is an app secret?
 
 Never store a password or other sensitive values in your source code. Get those values from an environment variable or a secret management system like: 
 - [Secret Manager](https://learn.microsoft.com/en-us/aspnet/core/security/app-secrets) for local development secrets.
 - [Azure Key Vault](https://learn.microsoft.com/en-us/azure/key-vault/general/overview) for cloud and production secrets.
 
+# Database connection strings
+
+Connection strings: https://learn.microsoft.com/en-us/ef/core/miscellaneous/connection-strings