Example config stanzas and YML templates

[0xC0FFEEEE]

Issue #258 has got me thinking about how best to document the various different YML config stanzas, required/optional fields and expected values, as, particularly for detections, defining a rule definition from scratch (i.e. without contentctl new) is somewhat of a trial and error process.

I appreciate there are still a lot of planned enhancements and updating the documentation is probably (understandably) quite low in the list of priorities, however there is probably a good middle ground to help others begin to adopt contentctl, and hopefully feed back/provide contributions on further enhancements.

Couple of ideas that go hand-in-hand that I'd love to get your thoughts on @pyth0n1c :

1. Have contentctl init provide example YML definitions covering the various different stanzas, required/optional fields and expected values. For example it's not immediately apparent that the tags.message field is the risk message, or that enabled_by_default is a supported field. I've started this effort within a forked branch, primarily for my own benefit but I'd be happy to contribute back once it's got a bit more substance.
2. Enable the use of templated YML files for ease of use - It would be neat if build|validate|test ignored YML files beginning with an underscore so that we could provide some cookie cutter templates that can be copied and used to produce new detections, stories, etc...