Add a document to toOpenArray proc (#23905)

lib/system.nim

@@ -2790,6 +2790,18 @@ when not defined(js):
 
 proc toOpenArray*[T](x: seq[T]; first, last: int): openArray[T] {.
   magic: "Slice".}
+  ## Allows passing the slice of `x` from the element at `first` to the element
+  ## at `last` to `openArray[T]` parameters without copying it.
+  ##
+  ## Example:
+  ##   ```nim
+  ##   proc test(x: openArray[int]) =
+  ##     doAssert x == [1, 2, 3]
+  ##
+  ##   let s = @[0, 1, 2, 3, 4]
+  ##   s.toOpenArray(1, 3).test
+  ##   ```
+
 proc toOpenArray*[T](x: openArray[T]; first, last: int): openArray[T] {.
   magic: "Slice".}
 proc toOpenArray*[I, T](x: array[I, T]; first, last: I): openArray[T] {.

lib/system/indices.nim

@@ -110,6 +110,9 @@ proc `[]`*[Idx, T; U, V: Ordinal](a: array[Idx, T], x: HSlice[U, V]): seq[T] {.s
   ##   var a = [1, 2, 3, 4]
   ##   assert a[0..2] == @[1, 2, 3]
   ##   ```
+  ##
+  ## See also:
+  ## * `toOpenArray(array[I, T];I,I) <#toOpenArray,array[I,T],I,I>`_
   let xa = a ^^ x.a
   let L = (a ^^ x.b) - xa + 1
   result = newSeq[T](L)
@@ -136,6 +139,9 @@ proc `[]`*[T; U, V: Ordinal](s: openArray[T], x: HSlice[U, V]): seq[T] {.systemR
   ##   var s = @[1, 2, 3, 4]
   ##   assert s[0..2] == @[1, 2, 3]
   ##   ```
+  ##
+  ## See also:
+  ## * `toOpenArray(openArray[T];int,int) <#toOpenArray,openArray[T],int,int>`_
   let a = s ^^ x.a
   let L = (s ^^ x.b) - a + 1
   newSeq(result, L)