Add v1.5 announcement banner to v1 project page#2

Copilot wants to merge 4 commits intomainace-step/ace-step.github.io:mainfrom

copilot/add-new-model-link-to-old-pageace-step/ace-step.github.io:copilot/add-new-model-link-to-old-pageCopy head branch name to clipboard