We don't actually have a hard date for 2.0 anymore, so I'm removing those dates to make room for 1.13, 1.14, etc. Also updated the list of milestones with the current state. We're actually doing pretty darn good (considering there was a bit of a global pandemic to contend with!)
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## Summary of the Pull Request
Upload the roadmap for Windows Terminal 2.0 and link to it on the README.
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* [ ] Closes #xxx
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* [ ] Requires documentation to be updated
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