Merge pull request #12 from tatsuya6502/fix-gh10

Add `--lib` option to the second `cargo new` invocation

Author: tatsuya6502

second-edition/src/ch14-03-cargo-workspaces.md

@@ -137,7 +137,7 @@ members = [
 それから、`add-one`という名前のライブラリクレートを生成してください:
 
 ```text
-$ cargo new add-one
+$ cargo new add-one --lib
      Created library `add-one` project
 ```