message: Show example for 'cfg(feature="foo")' dependency alternative.
diff: @@ -508,11 +508,19 @@ If you want to know which cfg targets are available on your platform, run
  targets are available for another platform, such as 64-bit Windows,
  run `rustc --print=cfg --target=x86_64-pc-windows-msvc`.
  -Unlike in your Rust source code,
  -you cannot use `[target.'cfg(feature = "my_crate")'.dependencies]` to add
  -dependencies based on optional crate features.
  -Use [the `[features]` section](manifest.md#the-features-section)
  -instead.
  +Unlike in your Rust source code, you cannot use
  +`[target.'cfg(feature = "fancy-feature")'.dependencies]` to add dependencies
  +based on optional features. Use [the `[features]`
  +section](manifest.md#the-features-section) instead:
  +
  +```toml
  +[dependencies]
  +foo = { version = "1.0", optional = true }
  +bar = { version = "1.0", optional = true }
  +
  +[features]
  +fancy-feature = ["foo", "bar"]
  +```
  The same applies to `cfg(debug_assertions)`, `cfg(test)` and `cfg(prog_macro)`.
  These values will not work as expected and will always have the default value
  