doc/tutorial/basics: add per-page chapter headings

Change-Id: I9e0a6b5d1a1c820081b3f87c3871068ea042f889
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 [TOC](Readme.md) [Prev](selectors.md) [Next](emit.md)
 
+_References and Visibility_
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 # Aliases
 
 An alias defines a local macro.