Add example using R2DBC Query by Example.

Closes #613.

r2dbc/query-by-example/README.adoc

@@ -0,0 +1,35 @@
+== Spring Data R2DBC - Query-by-Example (QBE) example
+
+This project contains samples of Query-by-Example of Spring Data R2DBC.
+
+=== Support for Query-by-Example
+
+Query by Example (QBE) is a user-friendly querying technique with a simple interface.
+It allows dynamic query creation and does not require to write queries containing field names.
+In fact, Query by Example does not require to write queries using SQL at all.
+
+An `Example` takes a data object (usually the entity object or a subtype of it) and a specification how to match properties.
+You can use Query by Example with Repositories.
+
+[source,java]
+----
+interface PersonRepository extends ReactiveCrudRepository<Person, Long>, ReactiveQueryByExampleExecutor<Person> {
+}
+----
+
+[source,java]
+----
+Example<Person> example = Example.of(new Person("Jon", "Snow"));
+repo.findAll(example);
+
+
+ExampleMatcher matcher = ExampleMatcher.matching().
+    .withMatcher("firstname", endsWith())
+    .withMatcher("lastname", startsWith().ignoreCase());
+
+Example<Person> example = Example.of(new Person("Jon", "Snow"), matcher);
+repo.count(example);
+----
+
+This example contains shows the usage with `PersonRepositoryIntegrationTests`.
+