List git-forest dependencies in Readme

[unixorn]

Description

git-forest requires that Git.pm be installed. Closes #92

Type of changes

• A helper script
• A link to an external resource like a blog post or video
• Text cleanups/updates

Checklist:

• All new and existing tests pass.
• Any scripts added use #!/usr/bin/env interpreter instead of potentially platform-specific direct paths (#!/bin/sh is an ok exception)\
• Scripts are marked executable
• I have added a credit line to README.md for the script
• If there was no author credit in a script added in this PR, I have added one.
• I have confirmed that the link(s) in my PR are valid.
• I have read the CONTRIBUTING document.

License Acceptance

• This repository is Apache version 2.0 licensed (some scripts may have alternate licensing inline in their code) and by making this PR, I am contributing my changes to the repository under the terms of the Apache 2 license.

[qlty-cloud-legacy]

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