reword section on aarch64 targets

Author: pietroalbini

posts/2020-12-31-Rust-1.49.0.md

@@ -29,20 +29,48 @@ For this release, we have some new targets and an improvement to the test
 framework. See the [detailed release notes][notes] to learn about other
 changes not covered by this post.
 
-### aarch64 targets
+### 64-bit ARM Linux reaches Tier 1
 
-We have two big changes to three targets:
+The Rust compiler supports [a wide variety of targets][platform-support], but
+the Rust Team can't provide the same level of support for all of them. To
+clearly mark how supported each target is we created a tiering system:
 
-* [`aarch64-unknown-linux-gnu` is now Tier 1](https://github.com/rust-lang/rust/pull/78228)
-* [`aarch64-apple-darwin` is now Tier 2](https://github.com/rust-lang/rust/pull/75991)
-* [`aarch64-pc-windows-msvc` is now Tier 2](https://github.com/rust-lang/rust/pull/75914)
+* Tier 3 targets are technically supported by the compiler, but we don't check
+  whether their code build or passes the tests, and we don't provide any
+  prebuilt binaries as part of our releases.
+* Tier 2 targets are guaranteed to build and we provide prebuilt binaries, but
+  we don't execute the test suite on those platforms: the produced binaries
+  might not work or might have bugs.
+* Tier 1 targets provide the highest support guarantee, and we run the full
+  suite on those platforms for every change merged in the compiler. Prebuilt
+  binaries are also available.
 
-If you're not familiar with our "tiers" of support, you can read about that
-on our [platform support
-page](https://doc.rust-lang.org/stable/rustc/platform-support.html). In
-brief, Tier 1 is "guaranteed to work," Tier 2 is "guaranteed to build," and
-Tier 3 is "code exists but is not tested." If you're a 64-bit ARM user, these
-changes mean that Rust programs will work better on your platforms!
+Rust 1.49.0 promotes the `aarch64-unknown-linux-gnu` target to Tier 1 support,
+bringing our highest guarantees to users of 64-bit ARM systems running Linux!
+We expect this change to benefit workloads spanning from embedded to desktops
+and servers.
+
+This is an important milestone for the project: it's the first time a non-x86
+target reaches the highest level of Quality Assurance and support provided by
+the Rust Team, and we hope this will pave the way for more targets to reach
+Tier 1 in the future!
+
+Note that Android is not affected by this change as it uses a different Tier 2
+target.
+
+[platform-support]: https://doc.rust-lang.org/stable/rustc/platform-support.html
+
+### 64-bit ARM macOS and Windows reach Tier 2
+
+Rust 1.49.0 also features two targets reaching Tier 2 support:
+
+* The `aarch64-apple-darwin` target brings support for Rust on Apple M1 systems!
+* The `aarch64-pc-windows-mvc` target brings support for Rust on 64-bit ARM
+  devices running Windows on ARM!
+
+Developers can expect both of those targets to have prebuilt binaries
+installable with `rustup` from now on! The Rust Team is not running the test
+suite on those platforms though, so there might be bugs or instabilities.
 
 ### Test framework captures output in threads