Update README

Author: natarajaya

README.md

@@ -11,3 +11,34 @@ cluster is automically joined up.
 If the deployment is scaled *up* after the initial creation those new Pods will
 be automatically added. Scaling *down* does not automatically remove the Pods
 from the membership database at this time.
+
+## Building
+
+### Master
+
+On push/merge to master, CI will automatically build and push
+`gpii/couchdb-statefulset-assembler:latest` image.
+
+### Tags
+
+Create and push git tag and CI will build and publish corresponding`
+`gpii/couchdb-statefulset-assembler:${git_tag}` docker image.
+
+#### Tag format
+
+Tags should follow actual couchdb-statefulset-assembler version, suffixed by
+`-gpii.${gpii_build_number}`, where `gpii_build_number` is monotonically
+increasing number denoting Docker image build number,  starting from `0`
+for each upstream version.
+
+Example:
+```
+0.0.3-gpii.0
+0.0.3-gpii.1
+...
+0.0.4-gpii.0
+```
+
+### Manually
+
+Run `make` to see all available steps.