Add brief description of the model

[fdiblen]

Add brief description of how the model works and if possible add some diagrams. This information can be added to README.md or a separate file.

[lyashevska]

I have added model description to README.md

[lyashevska]

This relates to #25

[lyashevska]

wiki is not available in free and private repos, as soon as we change this I will add the wiki page.