PDF manual: add section titles to page right-facing page headers (ocaml#13802)

Fixes: ocaml#13800

Author: nojb

manual/src/macros.tex

@@ -164,7 +164,8 @@
 
 \pagestyle{myheadings}
 \def\partmark#1{\markboth{Part \thepart. \ #1}{}}
-\def\chaptermark#1{\markright{Chapter \thechapter. \ #1}}
+\def\chaptermark#1{\markboth{Chapter \thechapter. \ #1}{}}
+\def\sectionmark#1{\markright{\thesection. \ #1}}
 
 % nth