Ignore files from website generation

- ignore the results generated by the user guide notebook
- ignore the jupyter_execute folder, containing files from the notebook
  execution

Author: schroedtert

.gitignore

@@ -315,6 +315,8 @@ cython_debug/
 *.code-workspace
 
 docs/build
+docs/source/results_introduction
+docs/jupyter_execute
 pedpy/_version.py
 docs/source/ZENODO.rst
 notebooks/results_introduction