Fix syntax errors on Gradle usage

Author: amlcurran

README.md

@@ -24,7 +24,15 @@ Set-up
 
 The library is now only compatible with Gradle out of the box. To use this library in your project, either:
 
-* Add the dependency from Maven like so: `compile 'com.github.amlcurran.showcaseview:library:+5.0.0-SNAPSHOT'`. See above for more information
+* Add the dependency from Maven like so: `compile 'com.github.amlcurran.showcaseview:library:5.0.0-SNAPSHOT'`. You'll also need to add the Sonatype snapshots repository to your `repositories {}` tag like so:
+~~~
+repositories {
+    mavenCentral()
+    maven {
+        url 'https://oss.sonatype.org/content/repositories/snapshots'
+    }
+}
+~~~
 * Copy the library project into your Gradle project. In your settings.gradle, add the project (using the `include (':libary')` notation). Sync Gradle and then go ahead! 
 
 Is it worth using?