README: Update to RalfJung's suggestion...

...verbatim. Thanks :)

Author: timotree3

README.md

@@ -53,15 +53,7 @@ Install Miri via `rustup`:
 rustup component add miri
 ```
 
-### error: component 'miri' is unavailable for download (nightly)
-
-The development of rustc's internals is quite fast paced. Downstream projects that rely on nightly internals, particularly clippy, can break fairly often because of this.
-
-When such breakages occur the nightly release will be missing Miri. This is a trade-off compared with the other option of just not publishing the night's release, but does avoid blocking the rust nightly releases for people that don't need clippy/Miri.
-
-To mitigate the issues we have:
-* rustup will warn if the update is missing any components you currently have. This means you can no longer accidentally update to a no-Miri release. Once Miri is available again it'll update.
-* However, if you need latest nightly Miri you can use <https://rust-lang.github.io/rustup-components-history/> to find and install a dated nightly release e.g. `rustup install nightly-2018-12-06`.
+If `rustup` says the `miri` component is unavailable, that's because not all nightly releases come with all tools. Check out this website to determine a nightly version that comes with Miri and install that, e.g. using `rustup install nightly-2019-03-28`.
 
 Now you can run your project in Miri: