Add a capabilities example to the README.md file.

README.md

@@ -27,6 +27,30 @@ and this to your source code:
 use bitflags::bitflags;
 ```
 
+## Example
+
+Generate a flags structure:
+
+```rust
+use bitflags::bitflags;
+
+bitflags! {
+    struct Flags: u32 {
+        const A = 0b00000001;
+        const B = 0b00000010;
+        const C = 0b00000100;
+        const ABC = Self::A.bits | Self::B.bits | Self::C.bits;
+    }
+}
+
+fn main() {
+    let mut flags = Flags::A | Flags::B;
+    assert!(flags.contains(Flags::A));
+    flags.set(Flags::C, true);
+    assert!(flags.contains(Flags::A | Flags::C));
+}
+```
+
 ## Rust Version Support
 
 The minimum supported Rust version is 1.46 due to use of associated constants and const functions.