fixed documentation about viewModels. The key in xml should be view_m…

[Jakhotiya]

…odel instead of viewModel

Description

\Magento\Backend\Block\Template documents view models and how to use them in blocks. The key used in arguments was viewModel which is wrong. Changed it to view_model and added an extra line about how to call these view models

Manual testing scenarios

Changed comments. Hence not applicable

Contribution checklist

• [ x] Pull request has a meaningful description of its purpose
• [ x] All commits are accompanied by meaningful commit messages
• [ x] All new or changed code is covered with unit/integration tests (if applicable)
• [ x] All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

Hi @Jakhotiya. Thank you for your contribution.
Changes from your Pull Request will be available with the upcoming 2.2.5 release.