Minor documentation edit.

Number of rustc calls would depending on various circumstances. Two is misleading.

Author: SeanTAllen

src/doc/guide.md

@@ -354,7 +354,7 @@ Hello, world!
 Bam! We build our project with `cargo build`, and run it with
 `./target/hello_world`. This hasn't bought us a whole lot over our simple use
 of `rustc`, but think about the future: when our project has more than one
-file, we would need to call `rustc` twice, and pass it a bunch of options to
+file, we would need to call `rustc` more than once, and pass it a bunch of options to
 tell it to build everything together. With Cargo, as our project grows, we can
 just `cargo build` and it'll work the right way.