docs(web): document use of `InlinedOSKView`

[`InlinedOSKView`](https://github.com/keymanapp/keyman/blob/tests/web/e2ekmxkbds/web/src/engine/src/osk/views/inlinedOskView.ts) allows to show the osk embedded in the page. We have a [test page](https://github.com/keymanapp/keyman/blob/tests/web/e2ekmxkbds/web/src/test/manual/web/inline-osk/index.html) that shows how to use this, but nothing on help.keyman.com.