website: Update Learning gem5 Part 3

This has various updates based on new gem5 changes, fixes for markdown,
and general typo fixes.

Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Change-Id: Ibb71c667b2e0ec79bfcf003882439c2cb513e7d0
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/62071
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby Bruce <bbruce@ucdavis.edu>
12 files changed