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

Change-Id: I9e0a6b5d1a1c820081b3f87c3871068ea042f889
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 [TOC](Readme.md) [Prev](numberlit.md) [Next](bytes.md)
 
+_JSON Sugar and other Goodness_
+
 # String Literals
 
 CUE strings allow a richer set of escape sequences than JSON.