Warning on install... how do I add .h5p mime type to .htaccess?

I suppose it should be mentioned in README that you may need to add this to .htaccess manually.

The default for Drupal is to create .htaccess with 444 permission, not writable:
https://git.drupalcode.org/project/drupal/-/blob/02507ab71932f2b574c777a...

So only in a non-default setup this might work automatically.