message: Add some warnings/disclaimers about build-dependencies.
  Also add `autocfg` to the list.
diff: @@ -230,6 +230,12 @@ The build script **does not** have access to the dependencies listed in the
  build dependencies are not available to the package itself unless also
  explicitly added in the `[dependencies]` table.
  +It is recommended to carefully consider each dependency you add, weighing
  +against the impact on compile time, licensing, maintenance, etc. Cargo will
  +attempt to reuse a dependency if it is shared between build dependencies and
  +normal dependencies. However, this is not always possible, for example when
  +cross-compiling, so keep that in consideration of the impact on compile time.
  +
  ### Change Detection
  When rebuilding a package, Cargo does not necessarily know if the build script
  