Add a link to rollup-plugin-command

[Vehmloewff]

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/Vehmloewff/rollup-plugin-command

Please Describe Your Addition

This PR aims at adding rollup-plugin-command to the awesome list.

This plugin is very similar to rollup-plugin-execute, but has a couple distinguishing features.

• This plugin allows both shell commands to be run and functions to be called. rollup-plugin-execute only supports shell commands.
• This plugin has, unlike rollup-plugin-execute, an exitOnFail option. This is very important if you are using this plugin to run tests.

[Vehmloewff]

ping :)

[shellscape]