Add notebook to the docs page so it will now render in the docs build

Author: drbenvincent

docs/source/notebooks/index.md

@@ -42,6 +42,13 @@ its_pymc.ipynb
 its_covid.ipynb
 :::
 
+:::{toctree}
+:caption: Transfer Function Interrupted Time Series
+:maxdepth: 1
+
+tfits_single_channel.ipynb
+:::
+
 :::{toctree}
 :caption: Regression Discontinuity
 :maxdepth: 1