adding ovito pip install

.github/workflows/linux.yml

@@ -10,6 +10,7 @@ jobs:
     - uses: actions/checkout@v2
     - name: installing preliminaries
       run: sudo apt install blender python3
+      run: sudo python3 -m pip install ovito
     - name: package add-on
       run: make
     - name: install blender plugin