Update Intro_to_Mill_BlogVideo.adoc

docs/modules/ROOT/partials/Intro_to_Mill_BlogVideo.adoc

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 If you're interested in the fundamental ideas behind Mill, rather than the user-facing
-benefits discussed above, check out the page on xref:depth/design-principles.adoc[Mill Design Principles]
+benefits discussed above, check out the page on xref:depth/design-principles.adoc[Mill Design Principles].
 The rest of this page contains a quick introduction to getting start with using
 Mill to build a simple {language} program. The other pages of this doc-site go into
 more depth, with more examples of how to use Mill and more details of how the