[Chapel Merge] Add a doc comment for OS.errorCode

Branch: refs/heads/main
Revision: 0c01206
Author: daviditen
Link: Unavailable
Log Message:

Merge pull request #20668 from daviditen/errorCode-doc-comment

Add a doc comment for OS.errorCode

[reviewed by @dlongnecke-cray, thanks!]

Add a doc comment for OS.errorCode derived from the comment for
SysBasic.syserr.

Modified Files:
M modules/standard/OS.chpl

Compare: https://github.com/chapel-lang/chapel/compare/fd49e8eb835b...0c01206381df