CONTRIBUTING: updates for recent changes

Recently, we changed to have uncrustify installed using Poetry, so we
no longer need to install it manually.

Also recommend installing the Ubuntu ARM GCC package.

CONTRIBUTING.md

@@ -10,8 +10,7 @@ This is the recommended development environment used by the Pybricks maintainers
 - [Git SCM][git] any recent-ish version
 - [VS Code][vscode] latest version
 - [Python][python] v3.10.x
-- [Poetry][poetry] v1.x
-- [Uncrustify][uncrustify] v0.71.x
+- [Poetry][poetry] v1.8.x
 - [GNU ARM Embedded Toolchain][arm-gcc] v10-2020-q4
 - [GNU GCC][gcc] for host operating system
 - [GNU Make][make]
@@ -25,7 +24,6 @@ Optional:
 [vscode]: https://code.visualstudio.com/Download
 [python]: https://www.python.org/downloads/
 [poetry]: https://python-poetry.org/docs/
-[uncrustify]: http://uncrustify.sourceforge.net/
 [arm-gcc]: https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-rm/downloads
 [gcc]: https://gcc.gnu.org/
 [make]: https://www.gnu.org/software/make/
@@ -63,15 +61,12 @@ Then install tools like this:
 
 #### Ubuntu
 
-Some of the prerequisites are available as Debian packages. The correct version
-of `uncrustify` is available via the Pybricks PPA. The `build-essential` package
-gets the GCC compiler for the host system and Make.
+Some of the prerequisites are available as Debian packages.
 
-    sudo apt-add-repository ppa:pybricks/ppa
     sudo apt update
-    sudo apt install git python3 uncrustify build-essential
+    sudo apt install git python3 build-essential gcc-arm-none-eabi
 
-Other tools (VS Code, Poetry, ARM Embedded Toolchain, Docker) can be installed
+Other tools (VS Code, Poetry, Docker) can be installed
 via the recommended install methods found in the links above.
 
 #### Windows
@@ -98,7 +93,6 @@ $env:PATH="C:\cygwin64\bin;C:\Program Files (x86)\GNU Arm Embedded Toolchain\10
 
 #### macOS
 
-    brew install uncrustify
     brew instal libusb
     brew install --cask gcc-arm-embedded