Recommend serviceX for local runs

analyses/cms-open-data-ttbar/README.md

@@ -58,6 +58,14 @@ pixi run --environment local-cms-open-data-ttbar start
 This will install all of the software and launch a Jupyter lab session.
 You can then use the file navigator and terminal in Jupyter lab to navigate to this directory to run the analysis.
 
+**Note** Given the size of the files, when running locally you will probably want to set the `USE_SERVICEX` global configuration variable in the `analyses/cms-open-data-ttbar/ttbar_analysis_pipeline.ipynb` notebook to `True`
+
+```python
+USE_SERVICEX = True
+```
+
+This requires you to have a ServiceX configuration file on your machine.
+
 #### Instructions for paired notebook
 
 If you only care about running the `ttbar_analysis_pipeline.ipynb` notebook, you can completely ignore the `ttbar_analysis_pipeline.py` file.