Add the RX examples

Author: cescoffier

reactive-programming/.mvn/wrapper/maven-wrapper.properties

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+distributionUrl=https://repo1.maven.org/maven2/org/apache/maven/apache-maven/3.3.9/apache-maven-3.3.9-bin.zip

reactive-programming/README.md

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+# Very simple RX examples
+
+This project contains the RX examples given in the book. There are far from being a complete introduction to reactive
+ programming and RX-Java.
+ 
+ The examples are intended to be run directly from the _main_ method of the different classes. So, once imported in 
+ your IDE, you should be able to run them. Alternatively, you can package the project and run them using:
+  
+
+```
+java -cp target/reactive-programming-example-1.0-SNAPSHOT.jar FULLY_QUALIFIED_CLASS_NAME
+```
+
+For example:
+
+```
+java -cp target/reactive-programming-example-1.0-SNAPSHOT.jar io.vertx.book.rx.ObservableExample
+
+```
+
+## Packaging the project
+
+Just run:
+
+```
+./mvnw package
+```
+
+On Windows, use:
+
+```
+./mvnw.bat package
+```
+
+