Document inclusive ranges.

This provides documentation for rust-lang/rust#28237.

Author: Alexis Hunt

src/flow_control/for.md

@@ -26,6 +26,26 @@ fn main() {
 }
 ```
 
+Alternatively, `a..=b` can be used for a range that is inclusive on both ends.
+The above can be written as:
+
+```rust,editable
+fn main() {
+    // `n` will take the values: 1, 2, ..., 100 in each iteration
+    for n in 1..=100 {
+        if n % 15 == 0 {
+            println!("fizzbuzz");
+        } else if n % 3 == 0 {
+            println!("fizz");
+        } else if n % 5 == 0 {
+            println!("buzz");
+        } else {
+            println!("{}", n);
+        }
+    }
+}
+```
+
 ## for and iterators
 
 The `for in` construct is able to interact with an `Iterator` in several ways.