DATAJDBC-287 - Polishing.

Moved the converter into it's own enum demonstrating good practices.
Added `@ReadingConverter`.

Original pull request: #106.

src/main/asciidoc/jdbc.adoc

@@ -145,27 +145,45 @@ This also means references are 1-1 or 1-n, but not n-1 or n-m.
 If you have n-1 or n-m references, you are, by definition, dealing with two separate aggregates.
 References between those should be encoded as simple `id` values, which should map properly with Spring Data JDBC.
 
+
+[[jdbc.entity-persistence.custom-converters]]
 === Custom converters
-Custom coverters can be registered, for types that are not supported by default, by inheriting your configuration from `JdbcConfiguration` and overwriting the method `jdbcCustomConversions()`. 
+
+Custom converters can be registered, for types that are not supported by default, by inheriting your configuration from `JdbcConfiguration` and overwriting the method `jdbcCustomConversions()`.
+
 ====
 [source, java]
 ----
 @Configuration
 public class DataJdbcConfiguration extends JdbcConfiguration {
+
     @Override
     protected JdbcCustomConversions jdbcCustomConversions() {
-      return new JdbcCustomConversions(Arrays.asList(new Converter<TIMESTAMPTZ, Date>() {
+
+      return new JdbcCustomConversions(Collections.singletonList(TimestampTzToDateConverter.INSTANCE));
+
+    }
+
+    @ReadingConverter
+    enum TimestampTzToDateConverter implements Converter<TIMESTAMPTZ, Date> {
+
+        INSTANCE;
+
         @Override
         public Date convert(TIMESTAMPTZ source) {
-          //...
+            //...
         }
-      }));
     }
 }
 ----
 ====
+
 The constructor of `JdbcCustomConversions` accepts a list of `org.springframework.core.convert.converter.Converter`.
 
+Converters should be annotated with `@ReadingConverter` or `@WritingConverter` in order to control their applicability to only reading from or to writing to the database.
+
+`TIMESTAMPTZ` in the example is a database specific data type that needs conversion into something more suitable for a domain model.
+
 [[jdbc.entity-persistence.naming-strategy]]
 === `NamingStrategy`