- Update Nav file to incorporate links to new documents

Upload New 6 new training documents & Supporting Image files
-- train-overview.adoc
-- train-hlpf-create-issue.adoc
-- train-hlpf-create-branch-from-issue.adoc
-- train-hlpf-checkout-branch.adoc
-- train-hlpf-create-merge-request.adoc
-- train-hlpf-commit-change.adoc
15 new image files the new images/training folder