update instructions for cue schema checking

Author: douwe

README.Rmd

@@ -98,10 +98,11 @@ locations:
       - A24:B25
 ```
 
-We provide a json schema for the data guide, allowing you to check the validity of 
+We provide a cue schema for the data guide, allowing you to check the validity of 
 guides that you wrote. The schema is available in the package as 
-`system.file("extdata", "excelguide_schema.json", package = "excelDataGuide")`. To 
-check its validity against the schema you can use the [Polyglottal JSON Schema Validator](https://www.npmjs.com/package/pajv). More details can be found in the vignette (to be done, see below).
+`system.file("extdata", "excelguide_schema.cue", package = "excelDataGuide")`. To 
+check its validity against the schema you can use the [CUE](https://cuelang.org/docs/) validator. 
+More details can be found in the vignette (to be done, see below).
 
 ## Future work