Add note about implicit closure parameter

Signed-off-by: Ben Sherman <[email protected]>

docs/reference/syntax.md

@@ -954,4 +954,4 @@ The following legacy features were excluded from this page because they are depr
 
 - The `addParams` and `params` clauses of include declarations. See {ref}`module-params` for more information.
 - The `when:` section of a process definition. See {ref}`process-when` for more information.
-- The implicit `it` closure parameter
+- The implicit `it` closure parameter. See {ref}`script-closure` for more information.

docs/script.md

@@ -376,6 +376,16 @@ def result = counts.values().inject { sum, v -> sum + v }
 
 This way, the closure is fully "self-contained" because it doesn't access or mutate any variables outside of its scope.
 
+:::{note}
+When a closure takes a single parameter, the parameter can be omitted, in which case the implicit `it` parameter will be used:
+
+```groovy
+[1, 2, 3].each { println it }
+```
+
+However, this practice is deprecated and will not be supported in the future.
+:::
+
 ## Script definitions
 
 So far, we have been focusing on the basic building blocks of Nextflow code, like variables, lists, strings, and closures.