Feat/RSS adding Sketch Library RSS (#25)

* added initial RSS feed

* added link to install in readme

* updated URL to point to raw hosted file

* fixed xml declaration

* moved xml to slds server so headers can serve the file correctly

* added git ignore and readme update

* added new line at the end of file

Author: aweibel

.gitignore

@@ -0,0 +1,3 @@
+# Ignore thumbnail preview generation of Sketch file
+.DS_Store
+*/.DS_Store

README.md

@@ -6,7 +6,8 @@
 <p align="center">
 A collection of Sketch Libraries including <a href="https://www.lightningdesignsystem.com">Lightning Design System</a> components and design patterns.
 </p>
-<h3 align="center"><a href="https://github.com/salesforce-ux/design-system-ui-kit/archive/master.zip">» Download the latest kit now «</a></h3>
+<h3 align="center"><a href="sketch://add-library?url=https://www.lightningdesignsystem.com/sketch-library-rss.xml">» Install the latest kit as a Sketch Library now «</a></h3>
+<p align="center"><a href="https://github.com/salesforce-ux/design-system-ui-kit/archive/master.zip">or download the latest kit</a></p>
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