add sample connection string

docs/en/Entity-Framework-Core-Oracle.md

@@ -27,6 +27,11 @@ Oracle connection strings are different than SQL Server connection strings. So,
 
 You typically will change the `appsettings.json` inside the `.DbMigrator` and `.Web` projects, but it depends on your solution structure.
 
+A sample connection string for Oracle:
+```
+Data Source=localhost;User Id=myuser;Password=mypassword;
+```
+
 ## Re-Generate the Migrations
 
 The startup template uses [Entity Framework Core's Code First Migrations](https://docs.microsoft.com/en-us/ef/core/managing-schemas/migrations/). EF Core Migrations depend on the selected DBMS provider. So, changing the DBMS provider will cause the migration fails.