add usage in README

.gitignore

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+node_modules/

README.md

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-node-shorthash
-==============
+# shorthash
 
-get an unique short hash of a string
+A mini Node.js module to generate short, alpha-number, undecryptable and unique hash id from a long string (utf8 format).
+Use shorthash when you want to encrypt a string like a movie name or a people name to a short, unique and url friendly id.
+so with shorthash, you can build an id-string map. 
+instead of quering the id from db each time, you just calculate the id out on the fly. 
+it's quite convenient in many conditions if you want to build a site like (书本画)[http://shubenhua.com], a books search engine in China.
+
+
+## Usage
+
+#### less's more, no options, just unique the string. 
+
+```javascript
+
+var sh = require("shorthash");
+
+console.log(sh.unique('foobar@example.com'));
+// you will get: Z1bL2tE
+
+console.log(sh.unique('my name is really big big and big...'));
+// you will get: Z1TirWS
+
+console.log(sh.unique('万里长城永不倒。。。'));
+// you will get: 2r6EFF
+
+console.log(sh.unique('和平'));
+// you will get: 33NM
+
+```