Here you are able to enable the option to enter a CRM link of each customer and get more information when creating the orders.To enable this option, follow the next steps:
Go to Setup > Settings > Find Customer and click on CRM Link option.
Enter the information requested about the CRM such as name, description (If needed) and Default URL. Click on enable checkbox and finally Save.
Once you have this setting enable go to Customer "Advance" Setup to continue with the process of adding the CRM link to each customer.