Users can put additional cellml models in this directory. 
Once the project is built these will be available as pre-compiled models 
and can be used with --model <name of cellml file (without.cellml)>.

Please note: The additional cellml file cannot have the same name as one of the pre-included cellml files in src/cellml
as these would generate model code with conflicting names. 
In case you receive a compile error with regards to duplicate definitions, 
we suggest renaming the additional cellml files to avoid conflicts.