Added SDK links (#426)

Added links to the guide and api reference.

I almost forgot about the [class inheritance diagram](http://parseplatform.org/parse-php-sdk/graph_class.html) hidden gem.

Author: dplewis

CONTRIBUTING.md

@@ -8,6 +8,8 @@ When committing, keep all lines to less than 80 characters, and try to
 follow the existing style. Before creating a pull request, squash your commits
 into a single commit. Please provide ample explanation in the commit message.
 
+In addition there's a pretty cool [class inheritance diagram](http://parseplatform.org/parse-php-sdk/graph_class.html) you can check out as well.
+
 Installation
 ------------
 

README.md

@@ -6,6 +6,8 @@
 The Parse PHP SDK gives you access to the powerful Parse cloud platform
 from your PHP app or script.  Designed to work with the self-hosted Parse Server: https://github.com/parse-community/parse-server
 
+For more information on Parse and its features, see [the website](http://parseplatform.org), [the PHP guide](https://docs.parseplatform.org/php/guide/) or [API Reference](http://parseplatform.org/parse-php-sdk/namespaces/Parse.html).
+
 Please note that this documentation contains the latest changes that may as of yet be unreleased. To see the README for your release please use the list below.
 - [1.4.0 README](https://github.com/parse-community/parse-php-sdk/blob/1.4.0/README.md)
 - [1.3.0 README](https://github.com/parse-community/parse-php-sdk/blob/1.3.0/README.md)