How do you add a pattern that begins with '-'?

So, I'm trying to add a pattern that looks like this:

```
-----BEGIN RSA PRIVATE KEY-----
```

However, I keep getting the following error, regardless of the options I provide:

```
$ git secrets --add --literal --global '-----BEGIN RSA PRIVATE KEY-----'
error: unknown option `---BEGIN RSA PRIVATE KEY-----'
usage: git secrets --scan [-r|--recursive] [--cached] [--no-index] [--untracked] [...]
or: git secrets --scan-history
or: git secrets --install [-f|--force] []
or: git secrets --list [--global]
or: git secrets --add [-a|--allowed] [-l|--literal] [--global]
or: git secrets --add-provider [--global] [arguments...]
or: git secrets --register-aws [--global]
or: git secrets --aws-provider []

--scan Scans for prohibited patterns
--scan-history Scans repo for prohibited patterns
--install Installs git hooks for Git repository or Git template directory
--list Lists secret patterns
--add Adds a prohibited or allowed pattern, ensuring to de-dupe with existing patterns
--add-provider Adds a secret provider that when called outputs secret patterns on new lines
--aws-provider Secret provider that outputs credentials found in an ini file
--register-aws Adds common AWS patterns to the git config and scans for ~/.aws/credentials
-r, --recursive --scan scans directories recursively
--cached --scan scans searches blobs registered in the index file
--no-index --scan searches files in the current directory that is not managed by Git
--untracked In addition to searching in the tracked files in the working tree, --scan also in untracked files
-f, --force --install overwrites hooks if the hook already exists
-l, --literal --add and --add-allowed patterns are escaped so that they are literal
-a, --allowed --add adds an allowed pattern instead of a prohibited pattern
--global Uses the --global git config
```

Start at the `git secrets --add` command and trace how its pattern argument is passed to option parsing. Reproduce the command with the literal RSA-key pattern, then verify that a pattern beginning with `-` is accepted and appears correctly in `git secrets --list`.

Written by the indexing model from the issue text.