Move developer docs to GitHub Wiki?

[akshaydewan]

These docs haven't been updated in a while (and probably don't need to be updated frequently). Moreover, in most cases, developers would be interested in the latest version of the code, so maintaining older versions seems to be quite an overhead. (Anyone who needs help with older versions could ask in the chatroom).

We could just move the docs and setup instructions to the Github Wiki section of the main gocd repository.

@arvindsv @nyuday @ketan @GaneshSPatil @bdpiparva @maheshp @varshavaradarajan @jyotisingh Thoughts?

[jyotisingh]

@akshaydewan - Agree with the bit about not maintaining multiple versions for dev docs. IMO, its fine to stop versioning it. Github Wiki is simple enough tool for the need we have for dev docs. What I am not sure about is how would we handle broken links to existing dev docs urls.