Tweak Development Setup Instructions
Tweak Development Setup Instructions

- be explicit about versions of dependencies.
- rely on package managers for installing software.
- clarify use of Docker/Vagrant
- switch use the imperative consistently in the section titles as these are instructions.
- clarify OAuth configuration steps.

RaptorRCX/exercism.io,RaptorRCX/exercism.io,tejasbubane/exercism.io,tejasbubane/exercism.io,treiff/exercism.io,tejasbubane/exercism.io,treiff/exercism.io,treiff/exercism.io,RaptorRCX/exercism.io,RaptorRCX/exercism.io,tejasbubane/exercism.io,treiff/exercism.io