message: Update README to describe the new swizzling feature
diff: @@ -32,6 +32,32 @@ vectors"), meaning when transforming a vector with a matrix, the matrix goes
  on the left. This is reflected in the fact that cgmath implements the
  multiplication operator for Matrix * Vector, but not Vector * Matrix.
  +## Features
  +
  +### Swizzling
  +This library offers an optional feature called
  +["swizzling"](https://en.wikipedia.org/wiki/Swizzling_(computer_graphics))
  +widely familiar to GPU programmers. To enable swizzle operators, pass the
  +`--features="swizzle"` option to cargo. Enabling this feature will increase
  +the size of the cgmath library by approximately 0.6MB. This isn't an
  +issue if the library is linked in the "normal" way by adding cgmath as a
  +dependency in Cargo.toml, which will link cgmath statically so all unused
  +swizzle operators will be optimized away by the compiler in release mode.
  +
  +#### Example
  +If we have
  +```rust
  +let v = Vector3::new(1.0, 2.0, 3.0);
  +```
  +then `v.xyxz()` produces a
  +```rust
  +Vector4 { x: 1.0, y: 2.0, z: 1.0, w: 3.0 }
  +```
  +and `v.zy()` produces a
  +```rust
  +Vector2 { x: 3.0, y: 2.0 }
  +```
  +
  ## Limitations
  cgmath is _not_ an n-dimensional library and is aimed at computer graphics
  