doc: add note about requiring Rosetta

docs/developer-setup.md

@@ -21,6 +21,24 @@ xcode-select --install
 brew install openssl readline sqlite3 xz zlib
 ```
+### Step 1.5: Apple Silicon users only: install Rosetta
+
+If you are running Apple Silicon it's highly recommended that you install Rosetta. Many downstream tools still generate `amd64` binaries only, and even if the tools support `arm64`, `asdf` plugins also need to support it, which they may not yet.
+
+**Note**: You will likely hit many problems unless Rosetta is installed.
+
+Check if Rosetta is installed by checking if it is running with the following one-liner:
+
+```shell
+pgrep -q oahd && echo "Rosetta is present on the system and is running." || echo "Rosetta is not running."
+```
+
+If it is not running, it is likely that it is not installed, so continue with the installation steps:
+
+```shell
+softwareupdate --install-rosetta --agree-to-license
+```
+
 ### Step 2: Install `asdf`
 Installation instructions for `asdf` can be found at <https://asdf-vm.com/guide/getting-started.html#_1-install-dependencies>.