More build-manifest docs

Author: jyn514

src/tools/build-manifest/README.md

@@ -8,10 +8,9 @@ This gets called by `promote-release` <https://github.com/rust-lang/promote-rele
 
 ## Adding a new component
 
-There are several steps involved here.
 1. Add a new `Step` to `dist.rs`. This should usually be named after the filename of the uploaded tarball. See https://github.com/rust-lang/rust/pull/101799/files#diff-2c56335faa24486df09ba392d8900c57e2fac4633e1f7038469bcf9ed3feb871 for an example.
     a. If appropriate, call `tarball.is_preview(true)` for the component.
-3. Add a new `PkgType` to build-manifest. Fix all the compile errors as appropriate.
+2. Add a new `PkgType` to build-manifest. Fix all the compile errors as appropriate.
 
 ## Testing changes locally
 
@@ -30,5 +29,5 @@ Then, you can generate the manifest and all the packages from `build/dist` to
 
 ```sh
 mkdir -p build/manifest
-cargo +nightly run -p build-manifest build/dist build/manifest 1970-01-01 http://example.com nightly
+cargo +nightly run --release -p build-manifest build/dist build/manifest 1970-01-01 http://example.com nightly
 ```