(ERROR CFFI-toolchain requires ASDF 3.1!)

While installing cl21 I came across the following problem: 

```
(ERROR CFFI-toolchain requires ASDF 3.1!)
```

This is because Quicklisp Beta packages ASDF 2.26 as the latest version.

Could you please update your documentation so that users know to install the Quicklisp Alpha[0](http://alpha.quicklisp.org/quicklisp.lisp), which does package ASDF 3.
