Badge request: npm installed size

I see there is already a badge for bundle phobia that displays the [bundle size](https://github.com/badges/shields/issues/941) which is useful for front-end packages like [react](https://bundlephobia.com/result?p=react@16.3.2).

I would like to add a badge for package phobia that displays the total npm install size plus dependencies, which is useful for backend packages such as [express](https://packagephobia.now.sh/result?p=express@4.16.3) or desktop packages like [electron](https://packagephobia.now.sh/result?p=electron@2.0.2).

Right now I'm just redirecting to shields but I had [a suggestion](https://github.com/TypeStrong/ts-node/pull/594) to get put this on shields.io

Would you accept a PR if I created one? 😄

Start by reviewing the existing Bundlephobia badge referenced in the issue and the Packagephobia result endpoint for express or electron. Confirm how the badge should expose total npm install size including dependencies, then verify the generated badge against those examples.

Written by the indexing model from the issue text.