Instructions for --local --os development

docs/CONTRIBUTING.md

@@ -29,6 +29,8 @@ We will review PRs when possible and work with you to integrate your contributio
 
 ## Running Your Local Fork
 
+**Note: for anyone testing the new `--local`, `--os`, and `--local --os` modes: When you run `poetry install` you aren't installing the optional dependencies and it'll throw errors. To test `--local` mode, run `poetry install -E local`. To test `--os` mode, run `poetry install -E os`. To test `--local --os` mode, run `poetry install -E local -E os`. You can edit the system messages for these modes in `interpreter/terminal_interface/profiles/defaults`.**
+
 Once you've forked the code and created a new branch for your work, you can run the fork in CLI mode by following these steps:
 
 1. CD into the project folder by running `cd open-interpreter`.