Update CONTRIBUTING.md
`freeze.py` expects `environment.yml` to be in working directory - calling it from project root will not work since the file is in a different folder
@@ -175,7 +175,8 @@ See the subsections below for more detailed instructions.
an existing package, you should then run:
```bash
- python ./repo2docker/buildpacks/conda/freeze.py
+ cd ./repo2docker/buildpacks/conda/
+ python freeze.py
```
This script will resolve dependencies and write them to the respective `.frozen.yml`
