code for `cosine-sim` in the docs is incomplete

The definition of `cosine-sim` in the [docs](https://github.com/Bridgei2i/clojure-word2vec/blob/master/doc/intro.md) isn't a complete s-exp.  Luckily the function is defined in `examples.clj`:

``` clojure
(defn cosine-sim
  [model word1 word2]
  (let [rawvecfn  #(.getRawVector (.forSearch model) %)
        [a1 a2] (map rawvecfn [word1 word2])]
    (i-stat/cosine-similarity a1 a2)))
```
