chore: prepare v1-v2 domain switch

[slorber]

Motivation

Preparing the v1<->v2 domain switch:

• Update readme to reflect v2 install instructions
• Switch changelog names
• Keep v1 URLs link to v1 domain on v1.docusaurus.io
• Keep explicit v2.docusaurus.io domain for now
• Try to migrate some v1 links to v2 if it make sense

Once the v2 domain is on docusaurus.io, we'll add a server redirect on v2.docusaurus.io to docusarus.io, and remove the v2. prefix everywhere

[netlify]

[V1] Deploy preview success

Built with commit 88d53fe

https://deploy-preview-4475--docusaurus-1.netlify.app

[netlify]

Deploy preview for docusaurus-2 ready!

Built with commit 88d53fe

https://deploy-preview-4475--docusaurus-2.netlify.app

[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟢 Performance	96
🟢 Accessibility	96
🟢 Best practices	100
🟢 SEO	100
🟢 PWA	95

Lighthouse ran on https://deploy-preview-4475--docusaurus-2.netlify.app/

[github-actions]

Size Change: +45 B (0%)

Total Size: 575 kB

Filename	Size	Change
website/build/blog/2017/12/14/introducing-docusaurus/index.html	60.8 kB	+45 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
website/build/assets/css/styles.********.css	87.2 kB	0 B
website/build/assets/js/main.********.js	401 kB	0 B
website/build/docs/introduction/index.html	235 B	0 B
website/build/index.html	25.7 kB	0 B

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