DATAJDBC-555 - Document supported databases.

Original pull request: #225.

src/main/asciidoc/jdbc.adoc

@@ -169,13 +169,20 @@ There are a couple of things one might want to customize in this setup.
 === Dialects
 
 Spring Data JDBC uses implementations of the interface `Dialect` to encapsulate behavior that is specific to a database or its JDBC driver.
-By default the `AbstractJdbcConfiguration` tries to determine the database in use an register the correct `Dialect`.
+By default, the `AbstractJdbcConfiguration` tries to determine the database in use an register the correct `Dialect`.
 This behavior can be changed by overwriting `jdbcDialect(NamedParameterJdbcOperations)`.
 
-TIP: Dialects are resolved by [`JdbcDialectResolver`] from `JdbcOperations`, typically by inspecting `Connection`.
+TIP: Dialects are resolved by `JdbcDialectResolver` from `JdbcOperations`, typically by inspecting `Connection`.
 You can let Spring auto-discover your `Dialect` by registering a class that implements `org.springframework.data.jdbc.repository.config.DialectResolver$JdbcDialectProvider` through `META-INF/spring.factories`.
 `DialectResolver` discovers dialect provider implementations from the class path using Spring's `SpringFactoriesLoader`.
 
+If you use a database for which no dialect is available, then your application won’t startup. In that case, you’ll have to ask your vendor to provide a `Dialect` implementation. Alternatively, you can:
+
+1. Implement your own `Dialect`.
+2. Implement a `JdbcDialectProvider` returning the `Dialect`.
+3. Register the provider by creating a `spring.factories`  resource under `META-INF` and perform the registration by adding a line +
+`org.springframework.data.jdbc.repository.config.DialectResolver$JdbcDialectProvider=<fully qualified name of your JdbcDialectProvider>`
+
 [[jdbc.entity-persistence]]
 == Persisting Entities
 

src/main/asciidoc/preface.adoc

@@ -37,6 +37,19 @@ See the Spring framework https://spring.io/docs[home page] for more information.
 
 The Spring Data JDBC binaries require JDK level 8.0 and above and https://spring.io/docs[Spring Framework] {springVersion} and above.
 
+In terms of databases, Spring Data JDBC requires a <<jdbc.dialects,dialect>> to abstract common SQL functionality over vendor-specific flavours.
+Support for the following databases is bundled with Spring Data JDBC binaries:
+
+* DB2
+* H2
+* HSQLDB
+* MariaDB
+* Microsoft SQL Server
+* MySQL
+* Postgres
+
+If you use a different database then your application won’t startup. The <<jdbc.dialects,dialect>> section contains further detail on how to proceed in such case.
+
 [[get-started:help]]
 == Additional Help Resources