Added new Slack workspace to README

[marcesengel]

Hey,

to coordinate the work on the PR to use the new context API, I created a Slack workspace for this package and I think it might as well serve other purposes, such as help and an overall better community experience.

Would be happy to see this merged as soon as possible and I hope you aren't upset about me creating a workspace using this name. If you want to I can make you the owner/admin ASAP.

Best Regards,
DragonRaider5

[yahoocla]

Thank you for submitting this pull request, however I do not see a valid CLA on file for you. Before we can merge this request please visit https://yahoocla.herokuapp.com/ and agree to the terms. Thanks! 😄

[StorytellerCZ]

@DragonRaider5 How can you join that workspace?

[marcesengel]

@StorytellerCZ you can simply take the link (react-intl.slack.com) and register there. Alternatively you can join the workspace react-intl.slack.com using the Slack client.

[StorytellerCZ]

@DragonRaider5 Actually I need an invitation:

Don't have an account on this workspace yet?
Contact the workspace administrator for an invitation 

That is the problem with Slack spaces. They are inherently a closed spaces. Though I think there is a Heroku app that you can deploy to automatically send invites to people who request them.

[marcesengel]

Haha my bad - I didn't even know this. I just knew the principle from the parcel-bundler project, where they seem to use (and host) slackin for this purpose...

Maybe we should come up with an alternative to Slack? I found Flock, other ideas?

[StorytellerCZ]

Gitter is tight pretty closely to Github so that might work.

[marcesengel]

Thanks to @papasmile pointing me at the documentation, I now obtained a general invite link.
I'll update it in the README - then it should work!

[redonkulus]

nit: instead of saying "New", can it say "Slack" just because eventually it won't be New anymore.