[gitblit] Upgrade to latest version and add repo init feature

gitblit/README.md

@@ -1,5 +1,39 @@
-Provides a ready-to-use instance of [GitBlit](http://gitblit.com/). In order to allow for 
-future upgrades run the container with a volume mount of `/data`, such as:
+Provides a ready-to-use instance of [GitBlit](http://gitblit.com/). 
+
+## Basic usage
+
+Start the GitBlit container using
+
+    docker run -d -p 80:80 p 443:443 --name gitblit itzg/gitblit
+
+Access its web interface at the mapped HTTP (80) or HTTPS (443) port of the 
+Docker host. Login with the default credentials __admin__ / __admin__ .
+
+
+## Data volume
+
+In order to allow for future upgrades, run the container with a volume mount of `/data`, such as:
 
     docker run -d -p 80:80 p 443:443 -v /tmp/gitblit-data:/data --name gitblit itzg/gitblit
 
+## Initial repository creation
+
+As a convenience for cluster configuration management with git 
+(such as with [Spring Cloud Config](https://cloud.spring.io/spring-cloud-config/)), 
+you may specify the name of an initial repository to be owned by the 'admin' user.
+This can be enabled by passing the name of that repository via the environment
+variable `GITBLIT_INITIAL_REPO`, such as
+
+    -e GITBLIT_INITIAL_REPO=default
+
+## Custom configuration
+
+You can add or override any of the `*.properties` files for configuring GitBlit,
+typically `gitblit.properties`, by placing those files in a volume attached at
+`/config`, such as
+
+    -v $(pwd)/extra:/config
+
+The property files in that configuration directory will be renamed with the 
+suffix `.applied` to avoid overwriting manually modified configuration on
+the next container startup.