add readme file

README.md

@@ -0,0 +1,27 @@
+# Example of stateful job using Apache Flink Scala API 2.12 
+
+To build a fat-jar run:
+
+```bash
+sbt assembly
+```
+
+in the result you will a JAR file at target/scala-2.12/scala-212-savepoint-assembly-0.1.0-SNAPSHOT.jar
+
+Main class for the a Flink job: __com.github.novakovalexey.Main__
+
+# Switch Flink version
+
+In order to switch to Flink 1.15.x or later version, you need to remove second % (percent) sign in the SBT `libraryDependencies` for most of the Flink dependencies. For example:
+
+```scala
+"org.apache.flink" %% "flink-streaming-java"
+```
+change to 
+
+```scala
+"org.apache.flink" % "flink-streaming-java"
+```
+
+this will make SBT to not add a Scala version suffix like _2.12 to the end of artifactId when
+downloading from the Maven central.