add links to qualtrics documentation

docs/best_practices/online_studies/qualtrics.md

@@ -8,6 +8,16 @@ nav_order: 1
 
 # Qualtrics
 
+## Embedded data and query strings
+
+You can pass information to Qualtrics to store and use in your survey via query strings, for example the `callbackUrl` or the `assignmentId` of the Pool Tool.
+
+You can find the documentation about how to do so [here](https://www.qualtrics.com/support/survey-platform/survey-module/survey-flow/standard-elements/passing-information-through-query-strings/).
+
+The documentation about how to use Embedded Fields in Qualtrics can be found [here](https://www.qualtrics.com/support/survey-platform/survey-module/survey-flow/standard-elements/embedded-data/).
+
+## Callback URL setup example
+
 1. In your Qualtrics survey, create an `Embedded Data` field (Survey Flow > Add new element > Select Embedded Data) and name it the same as the url parameter that contains the `callbackUrl`. Qualtrics will automatically store the URL parameter in this embedded field.
    1. If you want to use a different name, [refer to the section 'Manually store URL parameter'](#manually-store-url-parameter).
 2. On the last page of your survey, you can