Easier hiding of first title

[xixixao]

Following up on #323, I don't love the oranda-hide class solution (breaks the readme's HTML structure, adds noise to the README.md which people might read in their editors). This can be done via custom CSS instead, but I think even better solution would be a config in oranda.json, since it's such a common problem.

CSS solution:

main > h1:first-of-type {
  display: none;
}