Updates link to Core documentation

The previous link redirects to Cocoapods home page, this commit updates
the link to more suitable documentation.

README.md

@@ -71,7 +71,7 @@ CocoaPods is composed of the following projects:
 | Status | Project | Description | Info |
 | :----- | :------ | :--- | :--- |
 | [![Build Status](http://img.shields.io/travis/CocoaPods/CocoaPods/master.svg?style=flat)](http://travis-ci.org/CocoaPods/CocoaPods) | [CocoaPods](https://github.com/CocoaPods/CocoaPods) | The CocoaPods command line tool. | [guides](https://guides.cocoapods.org)
-| [![Build Status](http://img.shields.io/travis/CocoaPods/Core/master.svg?style=flat)](http://travis-ci.org/CocoaPods/Core) | [CocoaPods Core](https://github.com/CocoaPods/Core) | Support for working with specifications and podfiles. | [docs](http://docs.cocoapods.org/cocoapods_core)
+| [![Build Status](http://img.shields.io/travis/CocoaPods/Core/master.svg?style=flat)](http://travis-ci.org/CocoaPods/Core) | [CocoaPods Core](https://github.com/CocoaPods/Core) | Support for working with specifications and podfiles. | [docs](https://guides.cocoapods.org/contributing/components.html)
 | [![Build Status](http://img.shields.io/travis/CocoaPods/cocoapods-downloader/master.svg?style=flat)](http://travis-ci.org/CocoaPods/cocoapods-downloader) |[CocoaPods Downloader](https://github.com/CocoaPods/cocoapods-downloader) |  Downloaders for various source types. |  [docs](http://docs.cocoapods.org/cocoapods_downloader/index.html)
 | [![Build Status](http://img.shields.io/travis/CocoaPods/Xcodeproj/master.svg?style=flat)](https://travis-ci.org/CocoaPods/Xcodeproj) | [Xcodeproj](https://github.com/CocoaPods/Xcodeproj) | Create and modify Xcode projects from Ruby. |  [docs](http://docs.cocoapods.org/xcodeproj/index.html)
 | [![Build Status](http://img.shields.io/travis/CocoaPods/CLAide/master.svg?style=flat)](https://travis-ci.org/CocoaPods/CLAide) | [CLAide](https://github.com/CocoaPods/CLAide) | A small command-line interface framework.  | [docs](http://docs.cocoapods.org/claide/index.html)