website: Added list of helpful help commands to Learning gem5

The 'Using the default configs' section of
the Learning gem5 tutorial was missing
a list of helpful help commands to use
when a user runs --help.

They are now added in.

Change-Id: Id1fa528b057c8832dfee7d517ef7458aeba1c781
Jira: https://gem5.atlassian.net/browse/GEM5-462
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/28087
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: Jason Lowe-Power <power.jg@gmail.com>
1 file changed