Adding tutorial on Primary Data Analysis

[wpotrzebowski]

• Adds a Jupyter notebook tutorial for Primary Data Analysis with SasView (notebooks/PrimaryDataAnalysis/), adapting the sastutorials.org material to the SasView Python stack (sasdata, sasmodels/bumps, matplotlib).
• Covers data loading, interactive Guinier analysis ,SasView guinier cross-check, and Kratky / dimensionless Kratky plots.
• Includes three student challenges (RNase A, MAP2, pH-dependent discoidal particles) with guiding questions rather than spoilers, plus the accompanying example datasets.

General question: Is the tutorial repo a right place for such content?