Improve bundling/minification recommendations

[welingtonms]

Solves lit.dev's #1161

• Inform developers that the terser configuration is targeting the docs static site generation
• Refer to the Lit site for best practices on publishing Web Components and applications that include them.

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[AndrewJakubowicz]

Hi! Thanks for the pull request! The changes look great to me!

Unfortunately, the starter kit files are copied out of the main lit/lit repo from the packages subdirectory.
Would you be able to submit this PR to https://github.com/lit/lit modifying the files there: https://github.com/lit/lit/tree/main/packages/lit-starter-js

I think if this change is submitted here, then there is a risk in the future of the original README undoing your work.

[welingtonms]

Hi, @AndrewJakubowicz, thanks for letting me know about that!

Just opened the PR there.