README improvements

Cleaning up the README so that it's not extremely long but covers essential and useful information for getting started.

Changes:
- Improve wording in REAMDE.
- Remove documentation for command-line helpers from README (now in their own [wiki page](https://github.com/mongodb/mongo-orchestration/wiki/Command-Line-Interfaces))
- Fix up examples section in README.
- Add example of using `curl` with Mongo Orchestration.
- Show how to prettify JSON responses nicely & easily.
- Add installation instructions for `pip`.

https://github.com/lovett89/mongo-orchestration-1/blob/better-readme/README.md