message: Document new behavior of crates.io with the documentation field of the manifest
diff: @@ -41,6 +41,15 @@ building native code. More information can be found in the build script
  build = "build.rs"
  ```
  +## The `documentation` field (optional)
  +
  +This field specifies a URL to a website hosting the crate's documentation.
  +If no URL is specified in the manifest file, [crates.io][cratesio] will
  +automatically link your crate to the corresponding [docs.rs][docsrs] page.
  +
  +[docsrs]: https://docs.rs/
  +[cratesio]: https://crates.io/
  +
  ## The `exclude` and `include` fields (optional)
  You can explicitly specify to Cargo that a set of [globs][globs] should be
  