Fix missing install step in notebooks for documentation (Colab support) #134
Description
Switching to the new templates introduced a regression in documentation notebooks. The step that adds a hidden cell to install easydiffraction (if not already installed) is now missing.
This step is required to ensure that notebooks run correctly in environments like Google Colab, where the package may not be pre-installed.
We need to reintroduce this step in the documentation build process so that generated notebooks remain self-contained and executable.