Verify docs matches the latest SR changes

- add missing diagrams, fix figure links.
 - add section to run the registry as standalone service.
 - minor doc corrections.

 Resolves #16

docs/pom.xml

@@ -13,7 +13,7 @@
 	<name>Spring Cloud Schema Registry Docs</name>
 	<description>Spring Cloud Schema Registry Docs</description>
 	<properties>
-		<docs.main>spring-cloud-function</docs.main>
+		<docs.main>spring-cloud-schema-registry</docs.main>
 		<main.basedir>${basedir}/..</main.basedir>
 		<maven.plugin.plugin.version>3.4</maven.plugin.plugin.version>
 	</properties>