[sil_cameroon_qwerty] Size of welcome.htm file causes an issue on some devices

[darcywong00]

See keymanapp/keyman#4511

On some Android devices, the WebView for viewing the welcome.htm file becomes unresponsive. This can occur in either the Keyman for Android internal WebView, or with the ACTION_VIEW intent of viewing the file in Chrome 88.0 browser

Per @mcdurdin , maybe the 780kb file (before assets) needs to be split somehow.

Also applies to sil_cameroon_azerty

(low priority)