v0.1.2 Required data attribution

A correctness/compliance fix, no algorithm or numeric changes.

• Added the attribution required by Planet's Tanager STAC catalog terms (CC BY 4.0):
  NOTICE, README, the report and its PDFs, the notebook, and the repo's social preview
  image all now carry it.
• Added the citation required for ESA WorldCover 2021, also CC BY 4.0 and used to
  classify surface composition in the report.
• Added the acknowledgement AERONET's data-usage guidelines request, since aerosol
  reference values throughout the report come from it.
• run_tanager now emits a one-time reminder of the Tanager attribution requirement
  for anyone building their own outputs from the package.

No case-study numbers, figures, or conclusions changed.