How can I get the recoll package to index markdown (.md) files?

From what I understand markdown is pretty similar to text and html, which are all indexed by the [recoll](http://www.lesbonscomptes.com/recoll/) search engine. However my markdown files with extension .md are not being indexed. I have checked the filters and I am not sure which one applies to markdown, or if its support is missing altogether. If there is a simple way of manually creating a filter then it would be wonderful if someone could help me with creating one. Or if it is a simple setting I'm missing could you please point it out? I am running the latest version of recoll (1.21.5) on Debian Testing