Add auto-generated documentation

[morgante]

We should use the policy-tool to auto-generate documentation:

Auto-generated documentation could include:

1. Available constraint templates (all)
2. Available sample constraints
3. Available bundles and samples/constraints for each bundle

The documentation format can be based on the initial POC.

[morgante]

Potential implementation: a new make command which calls policy-tool and a Python script to generate the documentation from a jinja template.