add sequtils to prelude (#16431)

* add sequtils to prelude

i would argue that sequtils is used just as often as the other imports in prelude, and it'd be nice for it to be included.

* updated doc comment to add sequtils

* added sequtils import to changelog

changelog.md

@@ -70,6 +70,8 @@
   and `lists.toDoublyLinkedList` convert from `openArray`s; `lists.copy` implements
   shallow copying; `lists.add` concatenates two lists - an O(1) variation that consumes
   its argument, `addMoved`, is also supplied.
+  
+- Added `sequtils` import to `prelude`.
 
 ## Language changes
 

lib/prelude.nim

@@ -16,8 +16,8 @@
 ## Same as:
 ##
 ## .. code-block:: nim
-##   import os, strutils, times, parseutils, hashes, tables, sets
+##   import os, strutils, times, parseutils, hashes, tables, sets, sequtils
 ##   when not defined(js): import parseopt
 
-import os, strutils, times, parseutils, hashes, tables, sets
+import os, strutils, times, parseutils, hashes, tables, sets, sequtils
 when not defined(js): import parseopt