Clean up parent poms and clarify building and deploying

To deploy to snapshot repos you need

-DaltSnapshotDeploymentRepository=\
repo.spring.io::default::https://repo.spring.io/libs-snapshot-local

(as per /travis.yml) because the parent for spring-cloud-starter-parent
does not have a repository declared.

docs/src/main/asciidoc/README.adoc

@@ -4,4 +4,32 @@ include::intro.adoc[]
 
 include::https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/docs/src/main/asciidoc/contributing.adoc[]
 
+== Building and Deploying
+
+Since there is no code to compile in the starters they should do not need to compile, but a compiler has to be available because they are built and deployed as JAR artifacts. To install locally:
+
+----
+
+$ mvn install
+----
+
+and to deploy snapshots to repo.spring.io:
+
+----
+$ mvn install -DaltSnapshotDeploymentRepository=repo.spring.io::default::https://repo.spring.io/libs-snapshot-local
+----
+
+for a RELEASE build use
+
+----
+$ mvn install -DaltReleaseDeploymentRepository=repo.spring.io::default::https://repo.spring.io/libs-release-local
+----
+
+and for Maven Central use
+
+----
+$ mvn install -P central -DaltReleaseDeploymentRepository=sonatype-nexus-staging::default::https://oss.sonatype.org/service/local/staging/deploy/maven2
+----
+
+(the "central" profile is available for all projects in Spring Cloud and it sets up the gpg jar signing, and the repository has to be specified separately for this project because it is a parent of the starter parent which users in turn have as their own parent).