Spanner docs update (#494)

Adds spanner module docs and links

Author: balopat

docs/src/main/asciidoc/index-docinfo.xml

@@ -1,7 +1,7 @@
 <productname>Spring Cloud GCP</productname>
 <releaseinfo>{project-version}</releaseinfo>
 <copyright>
-	<year>2017</year>
+	<year>2017-2018</year>
 	<holder>Pivotal Software, Inc.</holder>
 </copyright>
 <legalnotice>

docs/src/main/asciidoc/index.adoc

@@ -1,6 +1,6 @@
 [[spring-cloud-gcp-reference]]
 = Spring Cloud GCP Reference Documentation
-João André Martins; Jisha Abubaker; Ray Tsang; Mike Eltsufin; Artem Bilan; Andreas Berger
+João André Martins; Jisha Abubaker; Ray Tsang; Mike Eltsufin; Artem Bilan; Andreas Berger; Balint Pato; Chengyuan Zhao
 :doctype: book
 :toc:
 :toclevels: 4
@@ -37,3 +37,5 @@ include::spring-integration.adoc[]
 include::trace.adoc[]
 
 include::config.adoc[]
+
+include::spanner.adoc[]

docs/src/main/asciidoc/pubsub.adoc

@@ -265,5 +265,5 @@ Google Cloud Pub/Sub API, if different from the ones in the
 <<spring-cloud-gcp-core,Spring Cloud GCP Core Module>> | Yes |
 | `spring.cloud.gcp.pubsub.credentials.scopes` |
 https://developers.google.com/identity/protocols/googlescopes[OAuth2 scope] for Spring Cloud GCP
-Config credentials | Yes | https://www.googleapis.com/auth/pubsub
+Pub/Sub credentials | Yes | https://www.googleapis.com/auth/pubsub
 |===