message: add note for user to create ARM_GCC_ROOT variable in vscode setup
diff: @@ -18,6 +18,7 @@ Before doing the VSCode setup, make sure you've installed all of your [prerequis
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  +1. Create an environment variable named `ARM_GCC_ROOT` whose value is the location of the `GNU Arm Embedded Toolchain` (.e.g `C:\Program Files (x86)\GNU Tools Arm Embedded\7 2018-q2-update`) that you installed in the prerequisites section of the developer's guide.
  1. Restart VSCode
  1. Open the VSCode Workspace file, which is located in the root of the ODrive repository. It is called `ODrive_Workspace.code-workspace`. The first time you open it, VSCode will install some dependencies. If it fails, you may need to [change your proxy settings](https://code.visualstudio.com/docs/getstarted/settings).
  