Update docs/navigation-structure.md

Co-Authored-By: Peter Mosses <18308236+pdmosses@users.noreply.github.com>

docs/navigation-structure.md

@@ -41,7 +41,9 @@ nav_order: 4
 The specified `nav_order` parameters on a site should be all integers or all strings.
 Pages without a `nav_order` parameter are ordered alphabetically by their `title`,
 and appear after the explicitly-ordered pages at each level.
-To sort all Capital letters before lowercase letters,
+By default, all Capital letters are sorted before all lowercase letters;
+adding `nav_sort: case_insensitive` in the configuration file ignores case
+when sorting strings (but also sorts numbers lexicographically: `10` comes before `1`).
 add `nav_sort: case_sensitive` in the configuration file.
 
 ---