Update documentation to reflect current features

• There are still mentions of a triage worksheet. "Cloudsplaining identifies violations of least privilege in AWS IAM policies and generates a pretty HTML report with a triage worksheet. It can scan all the policies in your AWS account or it can scan a single policy file." The worksheet is mentioned several times.
• As shown in the above, there is no mention of multiple AWS accounts
• The GIF still shows the original Cloudsplaining version, not the version with VueJS that looks much better.
• The list of risks in the second paragraph of the Overview does not include Credentials Exposure. These should also include links to the ReadTheDocs pages that include those definitions

Start with the documentation Overview and the sections containing the triage worksheet, account-scanning description, risk list, and GIF. Update the feature descriptions for multiple AWS accounts, remove outdated worksheet references, replace the GIF, and add Credentials Exposure with links to the relevant ReadTheDocs definitions.