+ "make doc" builds documentation in man and html formats; there are
+ also "make man", "make html" and "make info". Note that "make html"
+ requires asciidoc, but not xmlto. "make man" (and thus make doc)
+ requires both.
+
+ "make install-doc" installs documentation in man format only; there
+ are also "make install-man", "make install-html" and "make
+ install-info".
+