add Wikipedia link fro n-gram

README.md

@@ -415,7 +415,7 @@ See also [http://areweideyet.com/](http://areweideyet.com/) and [Rust and IDEs](
 
 * [BurntSushi/suffix](https://github.com/BurntSushi/suffix) — Linear time suffix array construction (with Unicode support) [<img src="https://travis-ci.org/BurntSushi/suffix.svg?branch=master">](https://travis-ci.org/BurntSushi/suffix)
 * [BurntSushi/tabwriter](https://github.com/BurntSushi/suffix) — Elastic tab stops (i.e., text column alignment) [<img src="https://travis-ci.org/BurntSushi/tabwriter.svg?branch=master">](https://travis-ci.org/BurntSushi/tabwriter)
-* [pwoolcoc/ngrams](https://github.com/pwoolcoc/ngrams) — Construct n-grams from arbitrary iterators [<img src="https://travis-ci.org/pwoolcoc/ngrams.svg?branch=master">](https://travis-ci.org/pwoolcoc/ngrams)
+* [pwoolcoc/ngrams](https://github.com/pwoolcoc/ngrams) — Construct [n-grams](https://en.wikipedia.org/wiki/N-gram) from arbitrary iterators [<img src="https://travis-ci.org/pwoolcoc/ngrams.svg?branch=master">](https://travis-ci.org/pwoolcoc/ngrams)
 * [rust-lang-nursery/regex](https://github.com/rust-lang-nursery/regex) — Regular expressions (RE2 style) [<img src="https://travis-ci.org/rust-lang-nursery/regex.svg?branch=master">](https://travis-ci.org/rust-lang-nursery/regex)
 
 ### Web programming