add cargo's git checkouts to the list of paths to mark as read-only in vscode

Author: programmerjake

editors/code/walkthrough-setup-tips.md

@@ -5,6 +5,7 @@ Add the following to settings.json to mark Rust library sources as read-only:
 ```json
 "files.readonlyInclude": {
   "**/.cargo/registry/src/**/*.rs": true,
+  "**/.cargo/git/checkouts/**/*.rs": true,
   "**/lib/rustlib/src/rust/library/**/*.rs": true,
 },
 ```