Documentation: list all possible options and more

[baruchiro]

Originally posted by @jossef in #107 (comment)

• Add a checkbox to the PR template to update README (yaml example) if needed
• Change the Commands section in the help message to Scan Commands
• Change the Flags section to Global Flags (only for global flags, of course)
• Use the linked PR as a source, and find a way to generate the flag tables from the source
• Build a FAQ page to document edge cases, such as gitleaks keywords, entropy, and stop words.
• Link to the release documentation. Since the README is updated with the latest commit, but a release is created manually, we need to add a link that says "If you're looking for the official documentation of the latest release" and put a lint to there.
• Explain the results structure