Add repo.readme parameter

This parameter can be used to specify a repo-specific includefile, which will
then be printed on the summary page for the repo.

If the parametervalue is a not an absolute path, it is taken to be relative
to repo.path.

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

cgit.h

@@ -68,6 +68,7 @@ struct repoinfo {
 	char *defbranch;
 	char *group;
 	char *module_link;
+	char *readme;
 	int snapshots;
 	int enable_log_filecount;
 	int enable_log_linecount;