Add git-side-by-side script

[unixorn]

Description

git-side-by-side does command line side by side diffs similar to github PRs.

Type of changes

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

Checklist

• I have read the CONTRIBUTING document.
• 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 allowed exception)
• Scripts added/updated in this PR are all marked executable.
• Scripts added/updated in this PR do not have a language file extension unless they are meant to be sourced and not run standalone. No one should have to know if a script was written in bash, python, ruby or whatever. Not including file extensions makes it easier to rewrite the script in another language later without having to change every reference to the previous version.
• I have added a credit line to README.md for any new scripts.
• If there was no author credit inside a script added in this PR, I have added one.
• I have confirmed that the link(s) in my PR are valid.

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]

Code Climate has analyzed commit b2d31ce and detected 0 issues on this pull request.

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[github-actions]

MegaLinter status: ⚠️ WARNING

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ COPYPASTE	jscpd	yes		no	1.1s
✅ CREDENTIALS	secretlint	yes		no	1.4s
✅ GIT	git_diff	yes		no	0.01s
⚠️ MARKDOWN	markdownlint	1		1	0.39s
⚠️ MARKDOWN	markdown-table-formatter	1		1	0.5s
✅ SPELL	misspell	2		0	0.06s

See errors details in artifact MegaLinter reports on CI Job page
Set VALIDATE_ALL_CODEBASE: true in mega-linter.yml to validate all sources, not only the diff