update web example demo

[ole3021]

Update the example of a serverless config file for

• keep it simple for most of bootstrap use cases /var/lang/${specific_lang}${version}/bin/${specific_lang} {enter_file}
• keep the availablily for users who need to fully customize the complex bootstrap file.

according to the changes above:

• if got 405 error, ask users to check Tencent SCF doc and add the customization bootstrap file.
• after deploy and bootstrap success, send error message if the port 9000 is not in use.

Things prefer to have.

• Provide complex bootstrap file demo in the help doc with explanation in comments.

[ole3021]

@yugasun please follow up the issue and merge if needed. (or drop is fine, this is a idea explantation PR)