CI: Update environment to pick up sphinx-build and other executables

Also install niworkflows into the environment

Author: effigies

.circleci/config.yml

@@ -542,6 +542,11 @@ jobs:
           command: |
             python -m pip install --no-cache-dir -U "pip>=20.3"
             python -m pip install --no-cache-dir -r docs/requirements.txt
+            eval "$(pyenv init -)"
+      - run:
+          name: Install Niworkflows
+          command: |
+            python -m pip install .
       - run:
           name: Build only this commit
           command: |