Add note on workspace perf

Author: mjbvz

release-notes/v1_96.md

@@ -131,6 +131,12 @@ Additionally, there is a new, experimental, setting to make an Inline Chat hint
 
 TODO@Tyriar
 
+### Performance improvements for `@workspace`
+
+When you use [`@workspace`](../docs/copilot/workspace-context.md) to ask Copilot about your currently opened workspace, we first need to narrow the workspace down into a set of relevant code snippets that we can hand off to Copilot as context. If your workspaces is backed by a GitHub repo, we can find these relevant snippets quickly by using Github code search. However as the code search index tracks the main branch of your repository, we couldn't rely on it for local changes or when on a branch.
+
+This iteration, we've worked bring the speed benefits of Github search to branches and pull requests. This means that we now search both the remote index based on your repo's main branch, along with searching any locally changed files. We then merge these results together, giving Copilot a fast and up to date set of snippets to work with. You can read more about Github code search and how to enable it [here](https://docs.github.com/en/enterprise-cloud@latest/copilot/github-copilot-enterprise/copilot-chat-in-github/using-github-copilot-chat-in-githubcom#asking-a-question-about-a-specific-repository-file-or-symbol).
+
 ## Accessibility
 
 ### Code Action accessibility signals