Add header and footers for hierarchical partial pooling (pymc-devs#393)

* Fix start and end of the files

* Fix start and end for ipynb

* Fix start and end for ipynb

* Fix start and end for ipynb

* Fix notebook name and watermark

* Pass pre-commit

* Add authorship

* Pre-commit checks

Co-authored-by: Alihan Zihna <[email protected]>

Author: 2 people