Add support for "readme" option

The value of this option is used as the default value for repo.readme.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

shared.c

@@ -62,7 +62,7 @@ struct cgit_repo *cgit_add_repo(const char *url)
 	ret->enable_subject_links = ctx.cfg.enable_subject_links;
 	ret->max_stats = ctx.cfg.max_stats;
 	ret->module_link = ctx.cfg.module_link;
-	ret->readme = NULL;
+	ret->readme = ctx.cfg.readme;
 	ret->mtime = -1;
 	ret->about_filter = ctx.cfg.about_filter;
 	ret->commit_filter = ctx.cfg.commit_filter;