Update requirements section of build_system/usage.txt

Author: bjorn3

build_system/usage.txt

@@ -43,7 +43,7 @@ REQUIREMENTS:
     * Rustup: By default rustup is used to install the right nightly version. If you don't want to
       use rustup, you can manually install the nightly version indicated by rust-toolchain.toml and
       point the CARGO, RUSTC and RUSTDOC env vars to the right executables.
-    * Git: `./y.sh prepare` uses git for applying patches and on Windows for downloading test repos.
+    * Git: Git is used for applying patches and on Windows for downloading test repos.
     * Curl and tar (non-Windows only): Used by `./y.sh prepare` to download a single commit for
       repos. Git will be used to clone the whole repo when using Windows.
     * [Hyperfine](https://github.com/sharkdp/hyperfine/): Used for benchmarking with `./y.sh bench`.