doc: install example .cfg files to $(docdir)/examples/

Change-Id: I8671ce33b9bf28c89f767dd1b4a1463aeb275158
diff --git a/Makefile.am b/Makefile.am
index 392d80d..f5062a2 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -1,6 +1,7 @@
 AUTOMAKE_OPTIONS = foreign dist-bzip2
 
 SUBDIRS = \
+	doc \
 	src \
 	sql \
 	tests \