update readme + bump version

PDFArchiver/Info.plist

@@ -21,7 +21,7 @@
 	<key>CFBundleShortVersionString</key>
 	<string>1.3.4</string>
 	<key>CFBundleVersion</key>
-	<string>49</string>
+	<string>50</string>
 	<key>ITSAppUsesNonExemptEncryption</key>
 	<false/>
 	<key>LSApplicationCategoryType</key>

README.md

@@ -84,6 +84,8 @@ Or clone the repository and build it:
 * Get in contact with us at [Slack](https://pdf-archiver.slack.com).
 
 ## :octocat: How to contribute
+Rate the App in the [Mac App Store](https://itunes.apple.com/app/id1352719750).
+
 All [contributions](https://github.com/PDF-Archiver/PDF-Archiver/blob/develop/.github/CONTRIBUTING.md) are welcome!
 Feel free to contribute to this project.
 Submit pull requests or contribute tutorials - whatever you have to offer, it would be appreciated!
@@ -92,5 +94,6 @@ Submit pull requests or contribute tutorials - whatever you have to offer, it wo
 * [**zngguvnf.org**](https://zngguvnf.org) discussing and creating this archive structure.
 * [**Karl Voit**](http://karl-voit.at/managing-digital-photographs/) for the initial idea of a document naming convention.
 * [**Nick Roach**](https://www.elegantthemes.com) for the [Icon](https://www.iconfinder.com/icons/1055071/document_file_icon).
+* MAS Preview Sound: [Love Jones by @nop](http://dig.ccmixter.org/files/Lancefield/50789)
 
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