Add docs about blacklist and progenitor option

[syou6162]

@z3z1ma I added documentation about the following features that were recently added to dbt-osmosis.

• blacklist feature via reserved _blacklist key in dbt-osmosis key under vars
  • ref: https://github.com/z3z1ma/dbt-osmosis/commit/97643dd765aa4a66980c85d1686e7e28deb689e4
• https://github.com/z3z1ma/dbt-osmosis/pull/83