Create documentation page for MS MARCO passage replication

[lintool]

This would be the pygaggle counterpart of: https://github.com/castorini/anserini/blob/master/docs/experiments-msmarco-passage.md

Let's name it docs/experiments-msmarco-passage.md to be consistent with Anserini. We'll add mutual references.

Let's start with monoBERT. Goal is for someone to be able to replicate monoBERT results following this doc. (At least on a subset.)

Plan is to run potential URAs through this document.