Link the rustc-dev-guide CLI chapter. (#384)

Author: ehuss

src/compiler/new_option.md

@@ -47,13 +47,16 @@ Once you've written up the proposal, you can [open a MCP](https://github.com/rus
 
 Naturally your new option will also have to be implemented. You can implement the option and open up a PR. Often, this implementation work actually happens **before** the MCP is created, and that's fine -- we'll just ask you to open an MCP with the write-up.
 
+See the [Command-line Arguments] chapter in the rustc dev guide for guidelines on how to name and define a new argument.
+
 A few notes that are sometimes overlooked:
 
 * Many options begin as "unstable" options, either because they use `-Z` or because they require `-Zunstable-options` to use.
 * You should document the option. Often this documentation can just be copied from the MCP text. Where you add this documentation depends on whether the option is available on stable Rust:
     * If it is unstable, then document the option in the [Unstable Book](https://doc.rust-lang.org/nightly/unstable-book/index.html), whose sources are in [src/doc/unstable-book](https://github.com/rust-lang/rust/tree/master/src/doc/unstable-book).
     * Once the option is stabilized, it should be documented in the [Rustc book](https://doc.rust-lang.org/rustc/index.html), whose sources as in [src/doc/rustc](https://github.com/rust-lang/rust/tree/master/src/doc/rustc). 
 
+[Command-line Arguments]: https://rustc-dev-guide.rust-lang.org/cli.html
 
 ## Stabilization and tracking issue