Add CI best practices to the readme

[rmri]

Please add CI best practices to the Readme file.

I've used different snapshotting tools in the past, where the workflow was to generate the images, then copy it to a certain location, usually a scheme agreed upon by the developer team and specify those file locations in the tests.

Swift SnapshotTesting does this automatically using the ___Snapshots___ folder but there's no mention of this in the readme, nor any mention how to customize this if you want to go with a custom folder structure.

I believe it would make life easier for many of us, so we don't have to read the source or search for issues.

[Brandon Williams]

Since this isn't an issue with the library and more of a feature request, I am going to convert it to a discussion.