Edit bssl-sys setup instructions.

Change-Id: I764551f842361b455f122287bcf7c4aef4b5cb82
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/63546
Auto-Submit: Cindy Lin <cinlin@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>

rust/bssl-sys/README.md

diff --git a/rust/bssl-sys/README.md b/rust/bssl-sys/README.md
index e2efd6c..c988813 100644
--- a/rust/bssl-sys/README.md
+++ b/rust/bssl-sys/README.md
@@ -7,6 +7,8 @@
 `bssl-sys` uses `bindgen` as part of the cmake build process to generate Rust compatibility shims for the targeted platform. It is important to generate it for the correct platform because `bindgen` uses LLVM information for alignment which varies depending on architecture.
 
 ### To Use
-Build `boringssl` with `-DRUST_BINDINGS=<rust-triple>` and ensure that you have `bindgen` installed. The `rust-triple` option should match the [Rust target triple](https://doc.rust-lang.org/nightly/rustc/platform-support.html) when building `bssl-sys`.
+1. Build `boringssl` with `-DRUST_BINDINGS=<rust-triple>`, which should match the [Rust target triple](https://doc.rust-lang.org/nightly/rustc/platform-support.html) when building `bssl-sys`,
+2. install `bindgen`, and
+3. install [`cargo-deny`](https://github.com/EmbarkStudios/cargo-deny).
 
-From there, the `bssl-sys` crate can be built. By default, it looks for `bindgen` output and BoringSSL static libraries in the `build` directory. This can be reconfigured with `BORINGSSL_BUILD_DIR` environment variable. Note the environment variable is evaluated relative to `rust/bssl-sys/src`, so using an absolute path may be more convenient.
+After that, the `bssl-sys` crate can be built. By default, it looks for `bindgen` output and BoringSSL static libraries in the `build` directory. This can be reconfigured with `BORINGSSL_BUILD_DIR` environment variable. Note the environment variable is evaluated relative to `rust/bssl-sys/src`, so using an absolute path may be more convenient.