Update documentation

Author: bgrana

README.md

@@ -16,11 +16,29 @@ This parser takes an xml Wirecloud config file and returns a javascript object c
 
 #### Initialization
 
-Before trying to get any data, the library must be imported and the parser object created:
+Before trying to get any data, the library must be imported and the parser object created. There are two ways of creating a parser object. One is to pass a path as parameter to the constructor and the parser will read and parse the file indicated by the path:
 
 ```javascript
 var Parser = require('wirecloud-config-parser');
-var configParser = new Parser('parse/to/file');
+var configParser = new Parser('path/to/file');
+```
+
+And the other is to give it an options object where you can specify either a path or directly the contents of a config file, as well as an option to validate the xml while building the object:
+
+```javascript
+var Parser = require('wirecloud-config-parser');
+var content = fs.readFileSync('path/to/file').toString();
+var configParser = new Parser({content: content, validate: true});
+```
+>**NOTE:** If you give both the path and  the content options in the object the parser will read from the file given in the path
+
+#### Validate
+
+Whether you have validated the XML content while building the object or not, you can use the validate function later to test if the XML complies with [Wirecloud's schema](https://raw.githubusercontent.com/Wirecloud/wirecloud/master/src/wirecloud/commons/utils/template/schemas/xml_schema.xsd):
+
+```javascript
+configParser.validate();
+// it should return true or false
 ```
 
 #### Retrieve data