Update HTML Module explainer wording around <script> elements

[trusktr]

This makes the wording imply that besides <script> element the HTML Module can contain any other elements, while explaining the same type=module requirement as before.

Modified

it is only allowed to contain <script> elements of type="module"

to

any <script> elements in the markup must be of type="module"

Reasoning: if an HTML Module were only allowed to contain script tags (of type module in this case) that would be boring!