Render markdown in YAML as HTML

[rjmackinnon]

The documentation says that if you set the contentType to "markdown" that it CAN render it as HTML, but it doesn't say how to get it to do that.

Operating System: (Windows or Linux or MacOS)
Windows

DocFX Version Used:
2.59.4.0

Template used: (default or statictoc or contain custom template)
LandingPageMulti.html.primary.tmpl.txt

Steps to Reproduce:

1. Define "content" as type "markdown".
2. Add field in YAML with simple markdown "[text](link)".

Expected Behavior:
Content renders as html.

Actual Behavior:
Content renders verbatim.