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

Change-Id: I9e0a6b5d1a1c820081b3f87c3871068ea042f889
diff --git a/doc/tutorial/basics/rangedef.md b/doc/tutorial/basics/rangedef.md
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--- a/doc/tutorial/basics/rangedef.md
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@@ -1,5 +1,7 @@
 [TOC](Readme.md) [Prev](ranges.md) [Next](lists.md)
 
+_Types and Values_
+
 # Predefined Ranges
 
 CUE numbers have arbitrary precision.