Documentation fix for Rust example

Change-Id: I68ad58a9b587c22705c40bcb63525ff581995184
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/6420
Reviewed-by: Petr Hosek <phosek@google.com>
Commit-Queue: Petr Hosek <phosek@google.com>

examples/rust_example/README.txt

diff --git a/examples/rust_example/README.txt b/examples/rust_example/README.txt
index 8bfbdd0..064e869 100644
--- a/examples/rust_example/README.txt
+++ b/examples/rust_example/README.txt
@@ -1,4 +1,4 @@
-This is an example directory structure that compiles some simple targets using
-gcc. It is intended to show how to set up a simple Rust GN build.
+This is an example directory structure that compiles a Rust hello world
+example. It is intended to show how to set up a simple Rust GN build.
 
 Don't miss the ".gn" file in this directory!