Add example to ALPHABET.md on how to diagnose a mis-matched alphabet

[KathyReid]

In ALPHABET.md we have the following information, which would be made stronger with an example. This Issue is to add information on how to diagnose a mis-matched alphabet.txt file - by providing a worked example.

### How to diagnose mis-matched alphabets?

If you think you used different alphabets to create a [language model and an acoustic model](AM_vs_LM.md), try decoding _without_ the scorer. If you can decode the audio without a scorer and the output is reasonable, but when you decode the same audio with a scorer, and the output is _not_ reasonable, then you could have mis-matched alphabets. Usually the easiest way to fix this is to re-compile the scorer with the correct alphabet.

[Read more information on building a language model (scorer)](SCORER.md).