output git command to show context for finding

**Is your feature request related to a problem? Please describe.**

To determine if a finding is a valid secret, some context of the found location is helpful.

When scanning a git repository, the file with the finding may have been removed, renamed, or the section with the finding removed or shifted. Opening the current version of the file often does not help to get the context

To get the context, the following git command can be used instead
```bash
git show [COMMIT-HASH] -L [LINENO-3],[LINENO+3]:[FILE_PATH]
```

All information for this command can be seen in the report from gitleaks. However, it can be a little annoying to assemble the command by hand

**Describe the solution you'd like**

Would it make sense to include this command in the console output for a finding, for quick copy/pasting?

**Describe alternatives you've considered**

- It is of course entirely possible to make a shell script for generating this command from a json report. But it might be nice to include this functionality in gitleaks itself.

- It took me quite a while to realize that this is actually easy to do with git. A short notice in the readme might suffice instead.

- Instead of the git command, a link to github/gitlab would also be helpful. It is possible to link to a specific line in a specific revision of a file. However, the link format for github and gitlab are different, and there is no simple way to determine whether a given git remote might be an enterprise github or gitlab server, so this would only work for repositories hosted on the default github or gitlab

**Additional context**

cc @zricethezav

The issue names no implementation file or test. Start by locating the console output for findings and the report fields containing the commit hash, line number, and file path; compare adding a copyable git show command with documenting the command in the README. Done means the chosen approach reliably helps recover context for removed, renamed, or shifted files.

Written by the indexing model from the issue text.