[JOSS review] Installation of single module requires previous folder creation

[ptmerz]

Minor thing, but took me way too long to understand what was going wrong:

In https://blaugroup.github.io/RNMC/Installation.html, you mention that one could build single modules by cd-ing into the respective folder and calling make MODULE there. This throws a non-descriptive linker error message, unless a directory called build was previously created.

It would be great if you could create this folder within your makefile. Otherwise, please at least assert for whether the folder is there and fail with a more informative error message.

[espottesmith]

This was addressed by #16.