chore: add roadmap (#1965)

README.md

@@ -29,6 +29,7 @@ the Rust programming language. It is:
 [Website](https://tokio.rs) |
 [Guides](https://tokio.rs/docs/) |
 [API Docs](https://docs.rs/tokio/latest/tokio) |
+[Roadmap](https://github.com/tokio-rs/tokio/ROADMAP.md) |
 [Chat](https://discord.gg/6yGkFeN)
 
 ## Overview

ROADMAP.md

@@ -0,0 +1,67 @@
+# Tokio Roadmap
+
+## A Roadmap to 1.0
+
+The question of "why not 1.0?" has come up a few times. After all, Tokio 0.1 has
+been stable for three years. The short answer: because it isn't time. There is
+nobody who would rather ship a Tokio 1.0 than us. It also isn't something to rush.
+
+After all, `async / await` only landed in the stable Rust channel weeks ago.
+There has been no significant production validation yet, except maybe fuchsia
+and that seems like a fairly specialized use case. This release of Tokio
+includes significant new code and new strategies with feature flags. Also, there
+are still big open questions, such as the [proposed changes][pr-1744] to
+`AsyncRead` and `AsyncWrite`.
+
+Tokio 1.0 will be released as soon as the APIs are proven to handle real-world
+production cases.
+
+### Tokio 1.0 in Q3 2020 with LTS support
+
+The Tokio 1.0 release will be **no later** than Q3 2020. It will also come with
+"long-term support" guarantees:
+
+* A minimum of 5 years of maintenance.
+* A minimum of 3 years before a hypothetical 2.0 release.
+
+When Tokio 1.0 is released in Q3 2020, on-going support, security fixes, and
+critical bug fixes are guaranteed until **at least** Q3 2025. Tokio 2.0 will not
+be released until **at least** Q3 2023 (though, ideally there will never been a
+Tokio 2.0 release).
+
+### How to get there
+
+While Tokio 0.1 probably should have been a 1.0, Tokio 0.2 will be a **true**
+0.2 release. There will breaking change releases every 2 ~ 3 months until 1.0.
+These changes will be **much** smaller than going from 0.1 -> 0.2. It is
+expected that the 1.0 release will look a lot like 0.2.
+
+### What is expected to change
+
+The biggest change will be the `AsyncRead` and `AsyncWrite` traits. Based on
+experience gained over the past 3 years, there are a couple of issues to
+address:
+
+* Be able to **safely** use uninitialized memory as a read buffer.
+* Practical read vectored and write vectored APIs.
+
+There are a few strategies to solve these problems. These strategies need to be
+investigated and the solution validated. You can see [this comment][pr-1744-comment] for a
+detailed statement of the problem.
+
+The other major change, which has been in the works for a while, is updating
+Mio. Mio 0.6 was first released almost 4 years ago and has not had a breaking
+change since. Mio 0.7 has been in the works for a while. It includes a full
+rewrite of the windows support as well as a refined API. More will be written
+about this shortly.
+
+Finally, now that the API is starting to stabilize, effort will be put into
+documentation. Tokio 0.2 is being released before updating the website and many
+of the old content will no longer be relevant. In the coming weeks, expect to
+see updates there.
+
+So, we have our work cut out for us. We hope you enjoy this 0.2 release and are
+looking forward to your feedback and help.
+
+[pr-1744]: https://github.com/tokio-rs/tokio/pull/1744
+[pr-1744-comment]: https://github.com/tokio-rs/tokio/pull/1744#issuecomment-553575438