Update documentation

README.md

@@ -6,6 +6,104 @@ Tools for suitable snapshot manipulation
 [![David](https://img.shields.io/david/bem-site/snapshot-master.svg)](https://david-dm.org/bem-site/snapshot-master)
 [![David](https://img.shields.io/david/dev/bem-site/snapshot-master.svg)](https://david-dm.org/bem-site/snapshot-master#info=devDependencies)
 
+## Usage
+
+### As npm package
+
+At first you should install npm package by:
+```
+$ npm install --save bem-site-snapshot-master
+```
+
+2 different strategies can be used via this package:
+
+* Simple
+* YDisk (snapshot operations performs also on Yandex Disk)
+
+Both strategies have the same API.
+
+#### API
+
+##### constructor
+
+You should create instance of snapshot master API class before using its methods.
+
+```
+var API = require('bem-site-snapshot-master').Simple,
+api = new API(options);
+
+// here you can call instance methods of API class
+api.getSnapshots(function (err) {
+    // TODO implement your handler
+});
+```
+
+`options` - is object with available fields:
+
+* `path` - full path to operation folder. (required).
+* `symlinks` - array with available symlink names (required).
+* `logger` - settings for logger module. See [Logger](https://www.npmjs.com/package/bem-site-logger) for more details.
+
+For YDisk API also `yandex-disk` options section needed:
+
+```
+'yandex-disk': {
+    user: 'john.smith',
+    password: '12345678',
+    namespace: 'test'
+}
+```
+
+##### getSnapshots
+
+Returns list of snapshot folder names.
+
+Arguments:
+* {Function} `callback` function
+
+##### getSnapshotNameForSymlink
+
+Returns name of snapshot which given symlink is pointed to
+
+Arguments:
+* {String} `symlink` - name of symlink
+* {Function} `callback` function
+
+##### getSnapshotDataForSymlink
+
+Retrieves data of snapshot which given symlink is pointed to and
+pipes it to destination stream
+
+Arguments:
+* {String} `symlink` - name of symlink
+* {String} `destination` - destination stream
+* {Function} `callback` function
+
+##### getSnapshotChanges
+
+Reads content of data.json file of given snapshot
+
+Arguments:
+* {String} `snapshot` - name of given snapshot
+* {Function} `callback` function
+
+##### switchSymlinkToSnapshot
+
+Switch symlink to folder with given snapshot name
+
+Arguments:
+* {String} `symlink` - name of symlink
+* {String} `snapshot` - name of given snapshot
+* {Function} `callback` function
+
+##### removeSnapshot
+
+Removes snapshot by given snapshot name
+
+Arguments:
+* {String} `snapshot` - name of given snapshot
+* {Function} `callback` function
+
 ## Testing
 
 Run tests: