docs: update REPL namespace documentation

PR-URL: #7406

Co-authored-by: Philipp Burckhardt <pburckhardt@outlook.com>
Reviewed-by: Philipp Burckhardt <pburckhardt@outlook.com>
Signed-off-by: stdlib-bot <82920195+stdlib-bot@users.noreply.github.com>

Author: stdlib-bot