Add concat files plugin to rollup awesome plugins (output list)

[kpulkit29]

Awesome Contribution Checklist:

• [x] I have read, and re-read the Contributing Guidelines
• [x] I have searched to ensure the suggested item doesn't exist on this list
• [x] This PR contains only one item

Please Provide a Link A Repository for Your Addition

https://github.com/kpulkit29/rollup-plugin-concatfiles

Please Describe Your Addition

Plugin to concatenate files/content to the generated output. This plugin would enable the user to concatenate files to the output or any other file in general.

[frank-dspeed]

LGTM +1

[shellscape]