message: Change README.md to reflect the current compiler situation
diff: @@ -45,9 +45,13 @@ will walk you through how to build from source on both macOS and Ubuntu.
  cd alacritty
  ```
  -3. Make sure you have the right Rust compiler installed. Alacritty is currently
  - pinned to a certain Rust nightly, and the compiler/nightly dependencies are
  - updated as needed. To install the correct compiler, run:
  +3. Make sure you have the right Rust compiler installed. Alacritty requires nightly Rust. Run
  +
  + ```sh
  + rustup override set nightly
  + ```
  +
  + If you run into problems, you can try a known-good version of the compiler by running
  ```sh
  rustup override set $(cat rustc-version)
  