modernize & improve the example in readme.md

[brodybits]

• used prettier-standard --lint to reformat the example, with semicolons removed, etc., but with 4-space indentation restored (by hand)
• replace var with const
• use destructured const to import the DOMParser object
• add blank lines
• move a console logging statement

triggered by discussion in issue #75

related to: PR #79 (add note about ES6 import)

✅ tested in a new npm package project in my work area

/cc @ajmas

[ajmas]

Looks good to me.

[karfau]

🤩