add command-line interface

[MFTabriz]

Add a command-line interface (CLI) to facilitate easier interaction with the library, enabling users to run it directly from the terminal. The CLI supports output in both JSON and human-readable formats. If any errors are encountered in the security.txt file, the program will exit with a status code of 1.

> sectxt --help
usage: sectxt [-h] [--json] [--show-notifications] [--show-recommendations] [--no-recommend-unknown-fields] [--version] address

Parse and validate security.txt

positional arguments:
  address               website URL or path to local file to check

options:
  -h, --help            show this help message and exit
  --json                output the results in JSON format
  --show-notifications  show notifications
  --show-recommendations
                        show recommendations
  --no-recommend-unknown-fields
                        do not issue notifications for unknown fields
  --version             show program's version number and exit

> sectxt --show-recommendation --show-notification ./security.txt 
[ERROR] L6: no_line_separators : Every line, including the last one, must end with either a carriage return and line feed characters or just a line feed character
[REC] no_encryption : 'Encryption' field should be present when 'Contact' field contains an email address.
[REC] not_signed : security.txt should be digitally signed.
[NOTE] L6: unknown_field : security.txt contains an unknown field. Field "test_unknown" is either a custom field which may not be widely supported, or there is a typo in a standardised field name.

> sectxt --show-recommendation --show-notification --json ./security.txt
[{'code': 'no_line_separators', 'message': 'Every line, including the last one, must end with either a carriage return and line feed characters or just a line feed character', 'line': 6, 'type': 'ERROR'}, {'code': 'no_encryption', 'message': "'Encryption' field should be present when 'Contact' field contains an email address.", 'line': None, 'type': 'REC'}, {'code': 'not_signed', 'message': 'security.txt should be digitally signed.', 'line': None, 'type': 'REC'}, {'code': 'unknown_field', 'message': 'security.txt contains an unknown field. Field "test_unknown" is either a custom field which may not be widely supported, or there is a typo in a standardised field name.', 'line': 6, 'type': 'NOTE'}]

[MFTabriz]

@DigitalTrustCenter Before proceeding to document this in the README file, I would appreciate your opinion on the following:

• Are the argument names clear and intuitive for users familiar with the library?
• What approach would you recommend for testing this functionality?

EDIT: I went ahead and added CLI information to the documentation.