Added example to load from CDN for browser

[gopiks]

Although there are separate examples to use IPFS in the browser, it makes sense to include the browser usage in the main README. Helps beginners to experiment easily.

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[achingbrain]

This is great and thank you for opening it, but js-IPFS is in the process of being deprecated, the replacement is Helia - please see the State of IPFS in JS post for a bit of background.

Could you open a similar PR against Helia?