Add Readme markdown support for linking to internal headers

In my mod's repo readme I have a link to an image at the bottom that works kind-of like a footnote:

In Raft, items you collect are added to the [first](#inventory-order) available slot in your inventory. Unfortunately,

...

# Inventory Order

![](ModResources/order.png)

This kind of link doesn't work for the site's mod Readme, so it's one more thing I have to change when my README.md gets updated.