feat(ios/samples): add third sample - inclusion of lexical model

> Nice. For bonus points, you can also add an example Tamil wordlist model. (I put one in the Android Samples (example.ta.wordlist.model.kmp)

Might be worth making as a third guide page. A simple keyboard-only guide is probably best as the base intro. I'll make that a separate issue for now.

_Originally posted by @jahorton in https://github.com/keymanapp/keyman/issues/4771#issuecomment-806311688_