Doesn't start as expected in the documentation

Followed the documentation; created a new virtual environment and then install galley; and then the following:

$ galley
usage: galley [-h] [--no-destroy] [config] [pattern]
galley: error: argument config: can't open '/Users/burhan/work/projects/django/docs/.galley.yml': [Errno 2] No such file or directory: '/Users/burhan/work/projects/django/docs/.galley.yml'

So what's this `.galley.yml`?

Review the documentation that instructs users to run `galley` and reproduce the setup in a virtual environment. Clarify what `.galley.yml` is, when it is needed, and how users should create or provide it; verify the documented command no longer produces an unexplained missing-file error.

Written by the indexing model from the issue text.