CONTRIBUTING: document GCC_10_ARM_NONE_EABI_BIN

This adds documentation for the GCC_10_ARM_NONE_EABI_BIN environment
variable to CONTRIBUTING.md and expands the explanation in
c_cpp_properties.json to cover Windows.

Author: dlech

.vscode/c_cpp_properties.json

@@ -10,6 +10,13 @@
 //    export GCC_10_ARM_NONE_EABI_BIN=/path/to/gcc-10-arm-none-eabi/bin/
 //
 // in .bashrc or .zshrc (trailing slash is required), then restart VS Code.
+//
+// On Windows, you can set this environment variable to (trailing slash is required):
+//
+//    C:\Program Files (x86)\GNU Arm Embedded Toolchain\10 2020-q4-major>code bin\
+//
+// via the System Properties. Restarting VS Code after this should be sufficient,
+// but you may need to log out and log back in if that doesn't work.
 
 {
     "env": {

CONTRIBUTING.md

@@ -159,6 +159,15 @@ working in the virtual environment. You should run `poetry shell` any time you
 open a new terminal window while working on `pybricks-micropython`.
 
 
+### Set up VS Code
+
+When using the Microsoft C/C++ extension for VS Code, you will need to set the
+`GCC_10_ARM_NONE_EABI_BIN` environment variable to the directory where the Arm
+toolchain was installed so that it can find the compiler to assist with code
+analysis. See [.vscode/c_cpp_properties.json](.vscode/c_cpp_properties.json)
+for more info.
+
+
 Building the code
 -----------------