Customise the generated Spec File

[icottambbc]

Hi maintainers. Love this project, big thumbs up.

I tried it for the first time last week and found myself needing to edit the generated spec file. The two edits required were:

1. Customise what's in the %build section of the spec file
2. Add the following macro to the top of the file: %global debug_package %{nil}

More context:

1. I need to customise what's in the %build section because i'm using yarn not npm. I tried to comply and use npm but i kept getting an error on the npm prune --production bit. It'd be very nice to be able to specify something custom in this section

2. TBH i'm not sure why i need this. My rpmbuild kept failing and this was the fix google told me to try and it worked.

Keen to hear your thoughts on this.