Inputs folder does not allow non-json file but cfn bundles it

# Description

I ran into this recently while setting up an example typescript cloudformation resource repository with a lot more tooling and documentation.

What I had wanted to do was add a README.md to that folder so that I could have better documentation for people looking through the directory.

As part of maturing this tool, I think it would be worth either providing a ".cfn-ignore" file or a hook for file copy transforms (the latter would be more valuable for things like adding comments to json but that may be a separate feature request).

I could implement the feature, but would like to submit this to see if there are strong opinions about the ignore file, etc.

Thanks in advance!