[request] include webpack browser bundle to npm package

Hi. I totally get that ["Packaging for browsers is currently highly experimental"](https://github.com/textileio/js-ipfs-lite#browser-1).

But to make it easier to play with.. would there be an objection to updating the [`prepublishOnly` npm script](https://github.com/textileio/js-ipfs-lite/blob/v0.1.5/package.json#L12)
* from:
```javascript
"prepublishOnly": "npm run build",
```
* to:
```javascript
"prepublishOnly": "npm run build && npm run browser:build",
```
* so for subsequent releases:
```html

```
- can be loaded from a CDN, such as:
* [jsdelivr](https://cdn.jsdelivr.net/npm/@textile/ipfs-lite@0.1.5/dist/)
* [unpkg](https://unpkg.com/browse/@textile/ipfs-lite@0.1.5/dist/)

- - - -

If the size the bundle adds to the npm package is an issue, then could it be attached to its corresponding [tagged release](https://github.com/textileio/js-ipfs-lite/releases)?

PS. If size is a concern, you may also consider adding an `.npmignore` file to exclude everything in the repo _except_ the `dist/` directory generated by the `build` tasks.