website: Fix several problems in Learning gem5 pages

- Update links to binaries in part1.6
- Fix page names in documentation.yml

Signed-off-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Change-Id: Ie71f62ec848f1a4b67fe9a02e9e4cc1ab3b191df
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/44205
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby R. Bruce <bbruce@ucdavis.edu>
2 files changed