Trim embedded git extras

Author: linhay

README.md

@@ -101,6 +101,7 @@ Embedded git bundle
 - To generate an updated bundle, run `tools/update-git-bundle.sh`. It writes to `tools/git-bundle/git-instance.bundle` by default.
 - If the bundle looks unusually large, run `tools/fix-git-bundle-links.sh` to relink duplicate `git-*` binaries and shrink the footprint.
 - Review the generated bundle and replace `Sources/SwiftGit/Resource/git-instance.bundle` if needed.
+- The default bundle is trimmed for size and omits GUI/web/perl tooling and shell completions. Use `--include-extras` to keep them.
 
 Tests and integration tests
 - Tests live under `Tests/SwiftGitTests/`.