Update index.mdx
Removes double "already" in sentence.
@@ -29,7 +29,7 @@ the free [Rust Book](https://doc.rust-lang.org/book/ch00-00-introduction.html) o
beginners and continues to be an excellent resource even for experienced Rust developers.
Ensure the latest version of Rust is installed by running `rustup update` or by
-[installing rust](https://www.rust-lang.org/tools/install) if you haven't already done so already.
+[installing rust](https://www.rust-lang.org/tools/install) if you haven't already done so.
After installing Rust, you can use Cargo to install `trunk` by running:
