Improve Mandatory check script and Readme

[WillemZeiler]

PR Description:

In this PR 2 files are adjusted to reflect a more realistic example, updated readme and updated screenshot:

Update script.js

• Adjusted the script to instead of not displaying the state field, flash the fields that are not filled in. This makes more sense and is using this existing function: https://www.servicenow.com/docs/bundle/zurich-api-reference/page/script/useful-scripts/reference/r_UsefulFieldScripts.html#d471717e187
• The getMissingFields() returns an array. Joining it with commas to improve readability of the info message.
• To prevent further execution added return statement.

Update README.md

• Highlighting what the code provides.
• Putting focus on the additional functionality of the error message that is provided by the function already, which was not mentioned in the original.
• Updated with 2 new screenshots

Pull Request Checklist

Overview

• Put an x inside of the square brackets to check each item.
• I have read and understood the CONTRIBUTING.md guidelines
• My pull request has a descriptive title that accurately reflects the changes and the description has been filled in above.
• I've included only files relevant to the changes described in the PR title and description
• I've created a new branch in my forked repository for this contribution

Code Quality

• My code is relevant to ServiceNow developers
• My code snippets expand meaningfully on official ServiceNow documentation (if applicable)
• [NA] I've disclosed use of ES2021 features (if applicable)
• I've tested my code snippets in a ServiceNow environment (where possible)

Repository Structure Compliance <- Existing files updated

• I've placed my code snippet(s) in one of the required top-level categories:
  • Core ServiceNow APIs/
  • Server-Side Components/
  • Client-Side Components/
  • Modern Development/
  • Integration/
  • Specialized Areas/
• I've used appropriate sub-categories within the top-level categories
• Each code snippet has its own folder with a descriptive name

Documentation

• I've included a README.md file for each code snippet
• The README.md includes:
  • Description of the code snippet functionality
  • Usage instructions or examples
  • Any prerequisites or dependencies
  • (Optional) Screenshots or diagrams if helpful

Restrictions

• My PR does not include XML exports of ServiceNow records
• My PR does not contain sensitive information (passwords, API keys, tokens)
• My PR does not include changes that fall outside the described scope

[snamjosh]

Thank you for your contribution.
g_form.flash() doesn't work in service portal.
can you please update readme to include same?
or you can use g_form.showFieldMsg() in your client script code so that it works on service portal as well.

[WillemZeiler]

Thank you for your contribution. g_form.flash() doesn't work in service portal. can you please update readme to include same? or you can use g_form.showFieldMsg() in your client script code so that it works on service portal as well.

@snamjosh the official documentation also does not include that remark https://www.servicenow.com/docs/bundle/zurich-api-reference/page/script/useful-scripts/reference/r_UsefulFieldScripts.html#d471717e187.

In addition, this script is in the Client script folder. There is a separate folder for Catalog client scripts.