Readme Rewrite

[malcyon]

The Readme is a bit confusing to try to navigate quickly. This is a rewrite of the Graylog Ansible Role documentation to bring more clarity and understanding to new users.

Fixes #158

[malcyon]

This is not quite done yet, but I am soliciting feedback on the format and contents. Any input is appreciated.

My priority was to make it easier for people quickly glancing through the page. I think the multiple examples were too confusing. I would like to have a single-instance playbook example and a clustering playbook example. Whether or not I get the second example done is contingent on me setting all that up.

I took the time to explicitely detail all the variables we have available. I would like to add more explanation on that page around what these settings do. The idea is to keep the casual user from having to dig through the code.

[malcyon]

Made some (mostly) minor suggestions, @malcyon. Good stuff.

Thanks! Much appreciated!

[malcyon]

There are a couple open issues around people trying to configure authentication in Elasticsearch and running into errors. It might be a good idea to have an example that sets that up. Or maybe the current example just needs to do that.

[malcyon]

I'm finding all sorts of random stuff, like:

• On Debian/Ubuntu, the Elasticsearch package is pinned to version 6.*. But it doesn't seem to do anything, as you can still install 7.10.2. And if I change it to pin 7.10*, it would potentially break people installing Graylog 3.3.
• The Elasticsearch setting action.auto_create_index is being set to True by default. But when I try to change it to False, I get a duplicate key error.

These will have to be separate PRs. Just noting them as things I found while reading over everything.