Examples in Help Output

[kchason]

Proposed changes

Addresses #3359 by adding the following text to the -help command:

EXAMPLES:
Run nuclei on single host:
	$ nuclei -target example.com

Run a scan with specific template directories:
	$ nuclei -target example.com -t cves/ -t panels/

Run nuclei against a list of hosts:
	$ nuclei -list hosts.txt

Run nuclei with a JSON output:
	$ nuclei -target example.com -json-export output.json

Run nuclei with sorted Markdown outputs (with environment variables):
	$ MARKDOWN_EXPORT_SORT_MODE=template nuclei -target example.com -markdown-export markdown/

Additional documentation is available at: https://nuclei.projectdiscovery.io/nuclei/get-started/#running-nuclei

Checklist

• Pull request is created against the dev branch
• All checks passed (lint, unit/integration/regression tests etc.) with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[kchason]

Is anything else needed on this?