Docs about custom types

docs/Solr.md

@@ -76,6 +76,23 @@ You can also copy the `thirdparty/`solr directory somewhere else,
 just set the path value in `mysite/_config.php` to point to the new location.
 And of course run `java -jar start.jar` from the new directory.
 
+### Custom Types
+
+Solr supports custom field type definitions which are written to its XML schema.
+Many standard ones are already included in the default schema.
+As the XML file is generated dynamically, we can add our own types
+by overloading the template responsible for it: `types.ss`.
+
+In the following example, we read out type definitions
+from a new file `mysite/solr/templates/types.ss` instead:
+
+	<?php
+	class MyIndex extends SolrIndex {
+		function getTypes() {
+			return $this->renderWith(Director::baseFolder() . '/mysite/solr/templates/types.ss');
+		}
+	}
+
 ## Debugging
 
 ### Using the web admin interface