Fix vale warnings in docs

The installer framework doc-snapshots built from the master branch is annotated to include the vale warnings. Use the toggle button on the top-right corner (next to the theme button) to view or hide annotations. When you hover the mouse pointer on an annotation/highlighted text block, you will see a pop-up with the warning message.

You could also see a summary report from vale in the diagnostics panel. Use the wrench icon on the top-right corner (next to the title on the index page) and choose the vale tab.