Add "Anti-feature" markers

Moved from https://github.com/awesome-foss/awesome-sysadmin/issues/623:

> On [this particular thread](https://github.com/awesome-foss/awesome-sysadmin/pull/618), it was mentioned that there may be a need to provide a disclaimer or flag for certain projects that have not-so-obvious caveats:

> I think adding `[xxxxx] features limited or restricted by licensing` flags and other disclaimers would be a valuable disclosure for people considering certain projects.

> This was driven by a conversation about https://sso.tax applicability to certain projects listed here.

Related to https://github.com/awesome-foss/awesome-sysadmin-data/issues/28

Start by reading the original awesome-sysadmin issue 623, the discussion in pull request 618, and related issue 28. Clarify the marker format, which caveats qualify, and how the disclaimers should be represented in this machine-readable data; done means an agreed, consistent anti-feature scheme is documented and applied as intended.

Written by the indexing model from the issue text.