message: Add a section "Before hacking on Cargo"
  The intent is redirecting contributor to know how we manage features and
  bugs and hope they start some discussions first.
diff: This chapter gives an overview of how to build Cargo, make a change, and
  submit a Pull Request.
  +0. [Before hacking on Cargo.](#before-hacking-on-cargo)
  1. [Check out the Cargo source.](#checkout-out-the-source)
  2. [Building Cargo.](#building-cargo)
  3. [Making a change.](#making-a-change)
  @@ -10,6 +11,15 @@ submit a Pull Request.
  5. [Submitting a Pull Request.](#submitting-a-pull-request)
  6. [The merging process.](#the-merging-process)
  +## Before hacking on Cargo
  +
  +We encourage people to discuss their design before hacking on code. This gives
  +the Cargo team a chance to know your idea more. Sometimes after a discussion,
  +we even find a way to solve the problem without coding! Typically, you
  +[file an issue] or start a thread on the [internals forum] before submitting a
  +pull request. Please read [the process] of how features and bugs are managed in
  +Cargo.
  +
  ## Checkout out the source
  We use the "fork and pull" model [described here][development-models], where
  @@ -143,3 +153,6 @@ more information on how Cargo releases are made.
  [homu-cargo]: https://buildbot2.rust-lang.org/homu/queue/cargo
  [homu-rust]: https://buildbot2.rust-lang.org/homu/queue/rust
  [release chapter]: release.md
  +[internals forum]: https://internals.rust-lang.org/c/tools-and-infrastructure/cargo
  +[file an issue]: https://github.com/rust-lang/cargo/issues
  +[the process]: index.md
  