Attempt to resolve doc testing errors

Author: Tyler Slabinski

doc/borrow_mut.md

@@ -5,23 +5,28 @@ corresponding to one of the fields of the decorated type.
 This allows types which contain some `T` to be passed anywhere that an
 `BorrowMut<T>` is accepted.
 
+Note that `BorrowMut<T>` expects the type to also implement `Borrow<T>`.
+
 # Newtypes and Structs with One Field
 
 When `BorrowMut` is derived for a newtype or struct with one field, a single
 implementation is generated to expose the underlying field.
 
 ```rust
+# use core::borrow::Borrow;
 # use core::borrow::BorrowMut;
 # #[macro_use] extern crate derive_more;
 # fn main(){}
-#[derive(BorrowMut)]
+#[derive(Borrow, BorrowMut)]
 struct MyWrapper(String);
 ```
 
 Generates:
 
 ```rust
+# use core::borrow::Borrow;
 # use core::borrow::BorrowMut;
+# #[derive(Borrow)]
 # struct MyWrapper(String);
 impl BorrowMut<String> for MyWrapper {
     fn borrow_mut(&mut self) -> &mut String {
@@ -37,7 +42,8 @@ implements all `BorrowMut` for all types that `Vec<i32>` implements `BorrowMut`
 ```rust
 # use core::borrow::BorrowMut;
 # #[macro_use] extern crate derive_more;
-#[derive(BorrowMut)]
+#[derive(Borrow, BorrowMut)]
+#[borrow(forward)]
 #[borrow_mut(forward)]
 struct SingleFieldForward(Vec<i32>);
 
@@ -51,6 +57,7 @@ fn main() {
 This generates:
 
 ```rust
+# #[derive(Borrow)]
 # struct SingleFieldForward(Vec<i32>);
 impl<__BorrowMutT: ?::core::marker::Sized> ::core::borrow::BorrowMut<__BorrowMutT> for SingleFieldForward
 where
@@ -72,13 +79,16 @@ An implementation will be generated for each indicated field.
 You can also exclude a specific field by using `#[borrow_mut(ignore)]`.
 
 ```rust
+# use core::borrow::Borrow;
 # use core::borrow::BorrowMut;
 # #[macro_use] extern crate derive_more;
 # fn main(){}
-#[derive(BorrowMut)]
+#[derive(Borrow, BorrowMut)]
 struct MyWrapper {
+    #[borrow]
     #[borrow_mut]
     name: String,
+    #[borrow]
     #[borrow_mut]
     num: i32,
     valid: bool,
@@ -90,7 +100,9 @@ struct MyWrapper {
 Generates:
 
 ```
+# use core::borrow::Borrow;
 # use core::borrow::BorrowMut;
+# #[derive(Borrow)]
 # struct MyWrapper {
 #     name: String,
 #     num: i32,
@@ -113,6 +125,7 @@ Note that `BorrowMut<T>` may only be implemented once for any given type `T`. Th
 mark more than one field of the same type with `#[borrow_mut]` will result in a compilation error.
 
 ```compile_fail
+# use core::borrow::Borrow;
 # use core::borrow::BorrowMut;
 # #[macro_use] extern crate derive_more;
 # fn main(){}