Prepare for 'about site' page / add 'root-readme' option to cgitrc

The new option names a file which will be included on a new page, next
to the current 'index' page.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>
diff --git a/ui-repolist.c b/ui-repolist.c
index 200640c..3f78e28 100644
--- a/ui-repolist.c
+++ b/ui-repolist.c
@@ -136,3 +136,9 @@
 		cgit_print_error("No repositories found");
 	cgit_print_docend();
 }
+
+void cgit_print_site_readme()
+{
+	if (ctx.cfg.root_readme)
+		html_include(ctx.cfg.root_readme);
+}