Add instructions for updating api docs

Author: lukebakken

APIDOCS.md

@@ -0,0 +1,8 @@
+# Updating API Documentation
+
+Updating the content in the `_site` submodule (which is this repository's `gh-pages` branch) is a manual process that must be done on Windows (as of docfx `2.31`):
+
+* `git submodule update --init` in this project
+* Run `docfx.exe` 2.31 or later
+* `cd _site` and commit all changes
+* `cd ..` and commit updated `_site` submodule