Add a bit about 'use' (#580)

* Add a bit about 'use'

* fix paths

src/modules/paths.md

@@ -9,3 +9,11 @@ Paths are resolved as follows:
 2. As an absolute path:
    * `crate::foo` refers to `foo` in the root of the current crate,
    * `bar::foo` refers to `foo` in the `bar` crate.
+
+A module can bring symbols from another module into scope with `use`.
+You will typically see something like this at the top of each module:
+
+```rust,editable
+use std::collections::HashSet;
+use std::mem::transmute;
+```