chore: Update Readme.md

[sumansaurabh]

This pull request includes changes to the README.md file that enhance the documentation for using penify-oapi-codegen from the command line. The changes provide additional examples for generating OpenAPI schema for all supported languages and for a specific language and variant. There's also a new command to get all supported languages. Additionally, the -s option has been replaced with -i for specifying the path to the OpenAPI schema file.

Here are the main changes:

• Added a new section for generating OpenAPI schema for all supported languages. It includes a command line example using penify-oapi-codegen with -i and -o options.
• Updated the section for generating OpenAPI schema for a specific language and variant. The command line example remains the same.
• Added a new section to get all supported languages. It includes a command line example using penify-oapi-codegen with -s option.
• Updated the Options section. The -s option has been replaced with -i for specifying the path to the OpenAPI schema file.…argument handling, and generate sample code for all languages and variants in OpenAPIHelper