Added Links to InterServer Slate Implementation

URL: https://my.interserver.net/apidoc/

Our implementation includes some minor customizations which others mind fight useful including icons for the Language tabs at the top right.

Side Note: The document contents including sample scripts , input/output parameter+descriptions, etc are generated entirely from a script i wrote that parses my SOAP API WSDL file, PHP Source (parsing phpdoc comments), and MySQL Table defintions (parsing field comments) to generate and populate all the neccesary info. At some point (faster if i have any requests for it ) ill make those scripts publicly available after i clean up the source a bit and make it more portable.

README.md

@@ -97,6 +97,7 @@ Examples of Slate in the Wild
 * [SafetyCulture API Documentation](https://developer.safetyculture.io/)
 * [hosting.de API Documentation](https://www.hosting.de/docs/api/)
 * [BlockCypher's API Documentation](http://dev.blockcypher.com)
+* [InterServer API Documentation](https://my.interserver.net/apidoc/)
 
 (Feel free to add your site to this list in a pull request!)