Add image optim plugin

[chrisdwheatley]

This PR adds the image optim plugin to the list of Netlify plugins. It also fixes an issue with the link to the plugins.json file not working from the readme.

[ehmicky]

Hi @chrisdwheatley,

This is great!

We have updated some things in how Build plugins are built. The new documentation is here. There is also a list of common gotchas here which is helpful to go through.

I think this plugin might be using the old format. Do you think it would be possible for you to update it? Thanks a lot for this awesome plugin!

[chrisdwheatley]

Thanks, unfortunately I've not had chance to take a look at how things have changed recently but will take a look over the weekend and try to get things up to date.

[ehmicky]

Great! Feel free to ask me any questions.

[ehmicky]

Hi @chrisdwheatley, I have put up some PRs to help out! :)

[chrisdwheatley]

I've updated and tested my plugin based on the changes you PR'd @ehmicky and I've published version 0.3.0. Hopefully that covers everything needed to be added to the list :)

The comment I mentioned originally about the readme link is no longer an issue just FYI.

[ehmicky]

Thanks @chrisdwheatley!
This is looking good. This repository's list of files has changed, which seemed to have messed up this PR diff a little. Would it be possible to only include the addition of this plugin to plugins.json.
Thanks!

[ehmicky]

🎉