doc: add license information for remark-cli

The LICENSE file was not originally included when remark-cli was
vendored. This Commit adds the LICENSE file back to tools/remark-cli
and updates the top level license in the project

PR-URL: https://github.com/nodejs/node/pull/16637


Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>