Add examples to some correctness lints

Author: BO41

clippy_lints/src/methods/mod.rs

@@ -889,6 +889,10 @@ declare_clippy_lint! {
     /// ```rust
     /// let _ = [1, 2, 3].into_iter().map(|x| *x).collect::<Vec<u32>>();
     /// ```
+    /// Could be written as:
+    /// ```rust
+    /// let _ = [1, 2, 3].iter().map(|x| *x).collect::<Vec<u32>>();
+    /// ```
     pub INTO_ITER_ON_ARRAY,
     correctness,
     "using `.into_iter()` on an array"

clippy_lints/src/swap.rs

@@ -52,6 +52,12 @@ declare_clippy_lint! {
     /// a = b;
     /// b = a;
     /// ```
+    /// Could be written as:
+    /// ```rust
+    /// # let mut a = 1;
+    /// # let mut b = 2;
+    /// std::mem::swap(&mut a, &mut b);
+    /// ```
     pub ALMOST_SWAPPED,
     correctness,
     "`foo = bar; bar = foo` sequence"