Adds v3.0.0 readme entry

Author: maciejlew

README.md

@@ -12,7 +12,7 @@ Add following in your project **pom.xml** file:
 <dependency>
     <groupId>pl.smsapi</groupId>
     <artifactId>smsapi-lib</artifactId>
-    <version>3.0.0-RC15</version>
+    <version>3.0.0</version>
 </dependency>
 ```