Slight changes from the book (#4077)

Not sure if this is the new format, but quickly looking I couldn't wind a easy way to update it in the book

# Objective

* For sample project to compile after first pages of book

got: 

```
  = note: clang: error: invalid linker name in argument '-fuse-ld=/usr/local/bin/zld'
          

error: linking with `cc` failed: exit status: 1
```

## Solution

FIx to correct zld path

.cargo/config_fast_builds

@@ -10,10 +10,10 @@ rustflags = ["-Clink-arg=-fuse-ld=lld", "-Zshare-generics=y"]
 # NOTE: you must manually install https://github.com/michaeleisel/zld on mac. you can easily do this with the "brew" package manager:
 # `brew install michaeleisel/zld/zld`
 [target.x86_64-apple-darwin]
-rustflags = ["-C", "link-arg=-fuse-ld=/usr/local/bin/zld", "-Zshare-generics=y"]
+rustflags = ["-C", "link-arg=-fuse-ld=/opt/homebrew/bin/zld", "-Zshare-generics=y"]
 
 [target.aarch64-apple-darwin]
-rustflags = ["-C", "link-arg=-fuse-ld=/usr/local/bin/zld", "-Zshare-generics=y"]
+rustflags = ["-C", "link-arg=-fuse-ld=/opt/homebrew/bin/zld", "-Zshare-generics=y"]
 
 [target.x86_64-pc-windows-msvc]
 linker = "rust-lld.exe"