Create a best practices document for secrets with running checks

[majormoses]

I see a lot of folks accidentally expose secrets in sensu by providing them directly in the command parameters. We should Talk about the dangers of such and how to properly use token substitution and redaction to prevent the leakage.

[majormoses]

ping @absolutejam.

My thoughts on an outline:

• what this is all about?
• what are the real dangers?
• what are the solutions?
• if there are good and bad try to illustrate both and why they might be a good/bad idea.
  There are definitely similarities lending a similar format to best practices on installing plugins #89