REVIEW: [NX-408] Add nexus karaf branding

https://issues.sonatype.org/browse/NX-408

```
Sonatype Nexus (3.0.0-SNAPSHOT)

Hit '<tab>' for a list of available commands
and '[cmd] --help' for help on a specific command.
Hit '<ctrl-d>' or 'system:shutdown' to shutdown.
```
NP, once the latest PRs are merged I'm going to go through and clean up the instructions to make sure it's all consistent and we only specify what's necessary.