update docs env to use opendrift branch too

Author: kthyng

docs/environment.yml

@@ -14,7 +14,7 @@ dependencies:
    - xarray
    - kerchunk==0.2.7
    - numpydoc
-   - opendrift ==1.13.0
+  #  - opendrift ==1.13.0
    # These are needed for the docs themselves
    - furo
    - jupytext
@@ -29,6 +29,7 @@ dependencies:
    - recommonmark
    - pip
    - pip:
+     - git+https://github.com/kthyng/opendrift.git@start_habs
      - particle-tracking-manager
      - docstring-inheritance
      - docrep<=0.2.7