fix: Set notebook cell timeout to 2 minutes (#61)

* To allow for long running processes that require actual computation
  extend the notebook cell timeout from the default 30 seconds to 120
  seconds (2 minutes).
   - c.f. https://jupyterbook.org/en/stable/customize/config.html

book/_config.yml

@@ -4,6 +4,9 @@ title: 'pyhf Tutorial'
 author: the pyhf development team
 logo: assets/pyhf-logo.svg
 
+execute:
+  timeout: 120  # seconds
+
 # HTML-specific settings
 html:
   use_repository_button: true