docs: add the documentation on the block template

[Arukuen]

fixes #3417

[github-actions]

🤖 Pull request artifacts

file	commit
pr3418-stackable-3418-merge.zip	8f36fa2

[github-actions]

Try this Pull Request in the WordPress playground: https://playground.wordpress.net/?mode=seamless#{"landingPage":"/wp-admin/post-new.php?post_type=page","preferredVersions":{"php":"latest","wp":"latest"},"steps":[{"step":"login","username":"admin","password":"password"},{"step":"installPlugin","pluginZipFile":{"resource":"url","url":"https://raw.githubusercontent.com/gambitph/Stackable/artifacts/pr3418-stackable-3418-merge.zip"}}]}

[Arukuen]

Added changes in the How to Create a New Block page.