Add developer Getting Started guide

First cut at the developer getting started guide.

Intended to replace:
- https://github.com/ManageIQ/cfme/wiki/Developer-Setup
- other private getting started docs
Let's capitalize keywords. also, I don't think you need createdb, and "CREATE USER" == "CREATE ROLE LOGIN"...so

```
psql -c "CREATE USER evm SUPERUSER PASSWORD 'secret'"
```