Hardened the post-build script.

[fdamken]

• Previously the post-build did not handle it if one did not pass any arguments (i.e. the project and target directory). This causes the variables to be empty and thus causes the script to work directly on the filesystem root (/), which is dangerous.
• I added set -o nounset to ensure no variables that are unset are able to be used.
• Besides that, I added information about those two parameters to the readme file.

[dsolmann]

Thanks, Merging!