No tools/apps directory when running example http3 server.

Message says to check tools/apps directory but there's no such directory.

Branch - Master

Steps -
1. Clone cloudfare / quiche.
2. Run the following command -

Finished `dev` profile [unoptimized + debuginfo] target(s) in 42.29s
Running `target/debug/examples/http3-server --cert ./quiche/examples/cert.crt --key ./quiche/examples/cert.key --listen '127.0.0.1:4433'`
Usage: target/debug/examples/http3-server

**See tools/apps/ for more complete implementations.**

3. Check directory using ls
~/git/https/quiche$ ls tools/apps
ls: cannot access 'tools/apps': No such file or directory

Start at the target/debug/examples/http3-server entry point and inspect the example's usage message that refers to tools/apps/. Check the repository tree for the current location of complete implementations; done means the message points to an existing location or no longer references the missing directory, and the example still displays correct usage.

Written by the indexing model from the issue text.