taken from here App Inventor Tutorials | Pura Vida Apps
Yes, you also can upload html files as assets into App Inventor! There is only one special thing to consider: During development, you have to use the development path to the embedded html document:
file:///mnt/sdcard/AppInventor/assets/<NAME OF YOUR HTML FILE>.html
Before packaging the app, use the production path.
file:///android_asset/<NAME OF YOUR HTML FILE>.html
however see also
so I’m not sure, if the AppInventor path is still valid in Makeroid…
Taifun