Update 13-looking-up-data.md

Updated link to crossref etiquette guidance

_episodes/13-looking-up-data.md

@@ -49,7 +49,7 @@ The next exercise demonstrates this two stage process in full.
 >* Give the column a name e.g. "Journal-Details"
 >* In the expression box you need to write some GREL where the output of the expression is a URL which can be used to retrieve data (the format of the data could be HTML, XML, JSON, or some other text format)
 >
->In this case we are going to use the CrossRef API: [https://api.crossref.org/](https://api.crossref.org/). Read more about the CrossRef service: [https://crossref.org](https://crossref.org). Note that API providers may impose rate limits or have other requirements for using their data, so it's important to check the site's documentation. To comply with API rate limits, use the Throttle Delay setting to specify the number of milliseconds between URL requests. CrossRef, for instance, [asks users](https://gitlab.com/crossref/rest_api/-/blob/main/resources/swagger/description.md#etiquette) to "specify a User-Agent header that properly identifies your script or tool and that provides a means of contacting you via email using 'mailto:'." User-agent headers provide administrators with user information that facilitates better administration and moderation of the API, and it is generally good etiquette to include a header with any API request.
+>In this case we are going to use the CrossRef API: [https://api.crossref.org/](https://api.crossref.org/). Read more about the CrossRef service: [https://crossref.org](https://crossref.org). Note that API providers may impose rate limits or have other requirements for using their data, so it's important to check the site's documentation. To comply with API rate limits, use the Throttle Delay setting to specify the number of milliseconds between URL requests. CrossRef, for instance, [asks users](https://www.crossref.org/documentation/retrieve-metadata/rest-api/tips-for-using-the-crossref-rest-api/#pick-the-right-service-level) to "specify a User-Agent header that properly identifies your script or tool and that provides a means of contacting you via email using 'mailto:'." User-agent headers provide administrators with user information that facilitates better administration and moderation of the API, and it is generally good etiquette to include a header with any API request.
 >
 >To edit your User-Agent header:
 >* Click 'Show' (next to 'HTTP headers to be used when fetching URLs'). Note that OpenRefine has already populated the 'User-Agent' field with information about the version of OpenRefine you are using; it should look similar to ``` OpenRefine 3... [...]``` (the information following ```OpenRefine``` will depend on the version of OpenRefine you are using).