docs: add reference to slim-sprig in the templating page (#2472)

Author: libor-m

website/src/docs/reference/templating.md

@@ -11,7 +11,8 @@ outline: deep
 Task's templating engine uses Go's
 [text/template](https://pkg.go.dev/text/template) package to interpolate values.
 This reference covers the main features and all available functions for creating
-dynamic Taskfiles.
+dynamic Taskfiles. Most of the provided functions come from the 
+[slim-sprig](https://sprig.taskfile.dev/) library.
 
 ## Basic Usage